UVa Solution 11192 - Group Reverse

#include<stdio.h>
#include<string.h>
int main()
{
    int p,i,j,top,G;
    char s1[105],s2[105];
    scanf("%d",&G);
    while(G)
    {
        scanf("%s",s1);
        int len=strlen(s1);
        p=len/G;
        top=0;
        for(i=p-1; i<len; i+=p)
        {
            for(j=i; j>i-p; j--)
                s2[top++]=s1[j];
        }
        s2[top++]=0;
        puts(s2);
        scanf("%d",&G);
    }
    return 0;
}
problem link: http://uva.onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=2133