Codeforces 731 B. Coupons and Discounts

B. Coupons and Discounts

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

The programming competition season has already started and it's time to train for ICPC. Sereja coaches his teams for a number of year and he knows that to get ready for the training session it's not enough to prepare only problems and editorial. As the training
sessions lasts for several hours, teams become hungry. Thus, Sereja orders a number of pizzas so they can eat right after the end of the competition.

Teams plan to train for n times during
n consecutive days. During the training session Sereja orders exactly one pizza for each team that is present this day. He already knows that there will be
ai teams on the
i-th day.

There are two types of discounts in Sereja's favourite pizzeria. The first discount works if one buys two pizzas at one day, while the second is a coupon that allows to buy one pizza during two
consecutive days (two pizzas in total).

As Sereja orders really a lot of pizza at this place, he is the golden client and can use the unlimited number of discounts and coupons of any type at any days.

Sereja wants to order exactly ai pizzas on the
i-th day while using only discounts and coupons. Note, that he will never buy more pizzas than he need for this particular day. Help him determine, whether he can buy the proper amount of pizzas each day if he is allowed
to use only coupons and discounts. Note, that it's also prohibited to have any active coupons after the end of the day
n.

Input
The first line of input contains a single integer n (1 ≤ n ≤ 200 000) — the number of training sessions.

The second line contains n integers
a1, a2, ...,
an (0 ≤ ai ≤ 10 000) — the number of teams that will be present on each of the days.

Output
If there is a way to order pizzas using only coupons and discounts and do not buy any extra pizzas on any of the days, then print "YES" (without quotes) in the only line of output. Otherwise, print "NO"
(without quotes).

Examples

Input

4
1 2 1 2

Output

YES

Input

3
1 0 1

Output

NO

Note
In the first sample, Sereja can use one coupon to buy one pizza on the first and the second days, one coupon to buy pizza on the second and the third days and one discount to buy pizzas on the fourth days. This is the only way to order pizzas for this sample.

In the second sample, Sereja can't use neither the coupon nor the discount without ordering an extra pizza. Note, that it's possible that there will be no teams attending the training sessions on some days.

题意：知道有N天，每天需要订ai个披萨，有两种优惠

1、直接买两个

2、买一个，预定明天一个相当于这个已经买了

问能不能用两种优惠满足每天的需要，并且不能买多。

ac code：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <list>
#include <deque>
#include <queue>
#include <iterator>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <cctype>
using namespace std;

#define si1(a) scanf("%d",&a)
#define si2(a,b) scanf("%d%d",&a,&b)
#define sd1(a) scanf("%lf",&a)
#define sd2(a,b) scanf("%lf%lf",&a,&b)
#define ss1(s) scanf("%s",s)
#define pi1(a) printf("%d\n",a)
#define pi2(a,b) printf("%d %d\n",a,b)
#define mset(a,b) memset(a,b,sizeof(a))
#define forb(i,a,b) for(int i=a;i<b;i++)
#define ford(i,a,b) for(int i=a;i<=b;i++)

typedef long long LL;
const int N=1100001;
const int M=6666666;
const int INF=0x3f3f3f3f;
const double PI=acos(-1.0);
const double eps=1e-7;
int a[200005];

int main()
{
int n;
cin>>n;
int flag=0;//判断是否需要预定
int fflag=1;//判断是否满足题目要求
for(int i=0;i<n;i++)
{
int cnt;
si1(cnt);
if(flag&&!cnt)
{
fflag=0;//昨天有预定但是今天不需要披萨，则不可能使用优惠
}
else if(cnt%2)
{
flag=!flag;//如果是奇数，那么表示需要预定或者是已经预定
}
}
if(flag) fflag=0;
if(fflag) printf("YES\n");
else
printf("NO\n");
return 0;
}