题解

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <map>
#include <cstring>
#include <iomanip>
#pragma GCC optimize(3)
const int N = 1e2+10;
const int INF = 0x3f3f3f3f;
using namespace std;
int len,a[N],ans,x;
bool f[1000]; 
int main()
{
	ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
	while(cin>>x && x!=-1)
	{
		len=0;
		ans=0;
		memset(a,0,sizeof(a));
		memset(f,0,sizeof(f));
		a[++len]=x;
		f[x]=1;
		int y=0;
		while(cin>>y && y)
		{
			a[++len]=y;
			f[y]=1;
		}
		for(int i=1;i<=len;i++)
		{
			if(f[a[i]*2]==1)
			{
				ans++;
			}
		}
		cout<<ans<<endl;
	}
	return 0;
}