#include <iostream>
using namespace std;

int main() {
    int arr[100][100] = {0,};
    int n;
    cin >> n;
    
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        for (int j = x; j < x + 10; j++) {
            for (int k = y; k < y + 10; k++) {
                arr[j][k] = 1;
            }
        }
    }

    int cnt = 0;
    for (int i = 0; i < 100; i++) {
        for (int j = 0; j < 100; j++) {
            if (arr[i][j] == 1) {
                cnt++;
            }
        }
    }
    
    cout << cnt;
    return 0;
}