#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    int md = 1000000007;
    
    cin >> n;
    
    unsigned long long c, d, ans = 0;
    for (int i = 0; i < n; i++) {
        cin >> c >> d;
        ans += static_cast<long long>(ceil(c / 2.0) * d) % md;
    }
    
    cout << setprecision(20) << ans % md << endl;
    
    return 0;
}