ACM (TJU) : 1930


// http://acm.tju.edu.cn/toj/showp1930.html

#include <stdio.h>

int main ()
{
    int a [18];

    while ( scanf ("%d", &a [0]) && a [0] != -1 ) {

        int n = 1;

        while ( scanf ("%d", &a [n]) && a [n] != 0 )
            n++;

        int count = 0;

        for ( int i = 0; i < n; i++ ) {
            for ( int j = 0; j < n; j++ ) {
                if ( a [i] == a [j] * 2 )
                    count++;
            }
        }

        printf ("%d\n", count);
    }

    return 0;
}

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