#include <bits/stdc++.h>
using namespace std;
 
int main() {
    int n;
    cin >> n;
    vector<int> a;
    map<int, int> mp;
    for(int i=0; i<n; i++){
        int x, y;
        cin >> x >> y;
        mp[x]++;
    }
    vector<int> k;
    for(auto &p : mp){
        if(p.second >= 2){
            int x = p.second;
            k.push_back(x);
        }
    }
    int s = 0;
    for(int x : k){
        x--;
        for(int i=0; i<=x; i++){
            s += i;
        }
    }
    cout << s;
    return 0;
}
 

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