#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
typedef long long ll;
const int mod=1e9+7;

int main(){
	int n; cin>>n;
	ll ans=0;
	rep(i,n){
		ll c,d; cin>>c>>d;
		if(c%2==0) ans+=(((c/2)%mod)*(d%mod))%mod;
		else ans+=(((c/2+1)%mod)*(d%mod))%mod;
	}
	cout<<ans%mod<<endl;
}