#include<iostream>
#define MOD (long long)1000000007
#define int long long
using namespace std;

signed main() {
int n, c, d;
int ans = 0;
cin >> n;
for( int i = 0; i < n; i++ ) {
cin >> c >> d;
ans += ((c+1)/2 )* d;
ans %= MOD;
}
cout << ans << endl;
return 0;
}