#include <iostream>
#include <map>
#include <algorithm>
using namespace std;
const int maxn = 100000;
int main()
{
    map<int, int> map;
    int n;
    cin >> n;
    for (int i = 0; i < n; i++)
    {
        int a, b;
        cin >> a >> b;
        if (map.find(a) != map.end())
        {
            map[a]++;
        }
        else
        {
            map.insert({a, 1});
        }
    }
    int ans = count_if(map.begin(), map.end(), [=](const pair<int, int> pair)
                       { return pair.second == 2; });

    cout << ans << endl;
    return 0;
}

#include <iostream>
#include <cstdio>
#include <map>
using namespace std;

int main() {
// freopen( "H:\命题\0 网站\3\Test\Input\input4.txt","r",stdin);
// freopen("H:\命题\0 网站\3\Test\Output\output4.txt","w",stdout);
int n;
cin>>n;
multimap<int,int> map;
for(int i=0; i<n; i++) {
int a,b;
cin>>a>>b;
map.insert((pair<int,int>(a,b)));
}
multimap<int,int>::iterator it=map.begin();
int ans=0;
while(it!=map.end()) {
int a=it->first, n=0;
while(it!=map.end() && it->first==a) {
n++;
it++;
}
if(n==2) ans++;
}
cout<<ans<<endl;
return 0;
}

#include <iostream>
#include <cstdio>
#include <map>
using namespace std;

int main() {
//  freopen(  "H:\\命题\\0 网站\\3\\Test\\Input\\input4.txt","r",stdin);
//  freopen("H:\\命题\\0 网站\\3\\Test\\Output\\output4.txt","w",stdout);
    int n;
    cin>>n;
    multimap<int,int> map;
    for(int i=0; i<n; i++) {
        int a,b;
        cin>>a>>b;
        map.insert((pair<int,int>(a,b)));
    }
    multimap<int,int>::iterator it=map.begin();
    int ans=0;
    while(it!=map.end()) {
        int a=it->first, n=0;
        while(it!=map.end() && it->first==a) {
            n++;
            it++;
        }
        if(n==2) ans++;
    }
    cout<<ans<<endl;
    return 0;
}