POJ 1298 The Hardest Problem Ever

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main()
{
char s1[110];
char s2[15];
int i,n;
while(1)
{
gets(s2);
if(strcmp(s2,"ENDOFINPUT")==0)
break;
else if(strcmp(s2,"START")==0)
{
gets(s1);
n=strlen(s1);
for(i=0;i<n;i++)
{
if(s1[i]>='A'&&s1[i]<='Z')
{
s1[i]='A'+(s1[i]-'A'-5+26)%26;
}
}
}
else if(strcmp(s2,"END")==0)
printf("%s\n",s1);
}
system("pause");
return 0;
}