若一头小母牛，从出生起第四个年头开始每年生一头母牛，按此规律，第n年有多少头母牛？

#include <stdio.h>
#include <stdlib.h>

int cow(int n)
{
int i, count, m = 1;
int A[3] = {0, 0, 0};
int tmp;
int pos;

for (i = 0; i < n; i++) {
pos = i % 3;
tmp = A[pos];
A[pos] = tmp + m;
m = m + tmp;
printf("year %d  1-%d, 2-%d, 3-%d --- %d\n",
i, A[0], A[1], A[2],  m);

}

count = m;
count += A[0] + A[1] + A[2];
return count;
}

int main(int argc, char *argv[])
{
printf("\n%s Years cow num %d\n", argv[1], cow(atoi(argv[1])));
return 0;
}