Doubles

http://poj.org/problem?id=1552

#include<stdio.h>
const int N=102;
int main()
{
    int n,f[N],g[N];
    int cnt;
    while(1)
    {
        cnt = 0;
        scanf("%d",&n);
        if (n==-1)
            break;
        f[0] = n;
        g[0] = 2*n;
        int i ;
        for ( i = 1;; i ++)
        {
            scanf("%d",&f[i]);
            if (f[i]==0)
                break;
            g[i] = 2*f[i];
        }
        for (int j = 0; j < i; j ++)
        {
            for (int k = 0; k < i; k ++)
            {
                if (f[j]==g[k])
                    cnt++;
            }
        }
        printf("%d\n",cnt);
    }
    return 0;
}