#include <algorithm>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#define rep(i, n) for (int i=0; i<n; ++i)
#define FOR(i, a, b) for (int i=a; i<b; ++i)
#define pb(x) push_back(x)
#define ll long long
#define ul unsigned long long
#define debug(x) cout  << #x << " : " << x << endl
#define out(x) cout << x
#define outl(x) cout << x << endl
#define int(n); int n; cin >> n;
#define llong(n); long long n; cin >> n;
#define s(s); string s; cin >> s;
#define into(a, n) for (int i = 0; i < n; ++i) cin >> a[i]
using namespace std;

const int inf =1500000000;
const int mod =1000000007; 
int main () {
  int(n);
  ll c[n], d[n];
  rep(i, n) cin >> c[i] >> d[i];
  ll res = 0, cnt[n];
  rep(i, n) {
    c[i] = (c[i] + 1) / 2;
    if (c[i] >= mod) c[i] %= mod;
    if (d[i] >= mod) d[i] %= mod;
    cnt[i] = c[i] * d[i];
    if (cnt[i] >= mod) cnt[i] %= mod;
  }
  
  rep(i, n) {
    res += cnt[i]; 
    if (res >= mod) res %= mod;
  }
  outl(res); 
   return 0;
}