#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>

#define INF 1000000000

using namespace std;
typedef long long ll;
const ll MOD = 1000000007;

int main(void) {
    int N;
    cin >> N;
    ll ans = 0;
    while (N--) {
        ll C, D;
        cin >> C >> D;
        ll tmp = (C+1) / 2;
        ans += ((tmp%MOD) * (D % MOD)) % MOD;
        ans %= MOD;
    }
    cout << ans << endl;
    return 0;
}