#include <iostream>
#include <cmath>

using namespace std;

int main() {
	ios::sync_with_stdio(false);
	int townsNo;
        while(cin >> townsNo) {
        	int *x = new int[townsNo];
		int *y = new int[townsNo];

            for (int i = 0; i < townsNo; i++) {
                cin >> x[i] >> y[i];
            }

            double pairs = townsNo * townsNo;
            int winner = 0;

            for (int i = 0; i < townsNo - 1; i++) {
                for (int j = i + 1; j < townsNo; j++) {
                    if (abs(x[i] - x[j]) == abs(y[i]  - y[j])){
                        winner += 2;
                    }
                }
            }

            cout << winner / pairs << endl;
        }
}