#include <bits/stdc++.h>
using namespace std;

int main(){
	int n;
	cin >> n;
	int total = 0;
	int c,d;
	for(int i = 0; i < n; i++){
		cin >> c >> d;
		c--;
		total += c * d;
	}
	cout << total << endl;
	return 0;
}