C++ :

#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int lights[2000005]={0};
    int n;
    cin >> n;
    for(int i = 1; i <= n; ++i){
        double a;
        int t;
        cin >> a >> t;
        for(int j = 1; j <= t; ++j){
            int r = int(a * j);
            lights[r] = !lights[r];
        }
    }

    for(int i = 1; i < 2000005; ++i){
        if(lights[i]){
            cout << i << endl;
            break;
        }
    }

    return 0;
}