简单题

#include 
      
       #include 
       
        #include 
        
         #include 
         
          using namespace std;#define maxn 20int n;int f[maxn];void input(){    n = 0;    while (scanf("%d", &f[n]), f[n])    {        if (f[n] == -1)            exit(0);        n++;    }}void work(){    int ans = 0;    for (int i = 0; i < n; i++)        for (int j = 0; j < n; j++)            if (f[i] == f[j] * 2)                ans++;    printf("%d\n", ans);}int main(){    while (1)    {        input();        work();    }}