#include <iostream>

using namespace std;

using ll = long long;
constexpr ll MOD = ((1e9) + 7);

int main()
{
    int N;
    ll res = 0;
    cin >> N;
    for (int i = 0; i < N; i++) {
        ll C, D;
        cin >> C >> D;        
        if (C & 1) {
            C %= MOD;
            D %= MOD;
            res += (C + 1) / 2 * D;
        } else {
            C %= MOD;
            D %= MOD;
            res += C / 2 * D;
        }
    }
    cout << res << endl;
    return 0;
}