#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  ll mod = 1000000007;
  int n;
  cin >> n;
  vector<ll> c(n);
  vector<ll> d(n);
  rep(i,n){
  	cin >> c[i] >> d[i];
  }
  ll ans=0;
  rep(i,n){
  	ll k;
  	if(c[i] % 2 == 0) k = c[i] / 2;
  	else k = (c[i] + 1) / 2;
  	ans += k * d[i] % mod;
  }
  cout << ans % mod << endl;
  return 0;
}