#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>
#include <sstream>
#include <map>
#include <queue>

using namespace std;
 
const long long mod = 1000000000+7;

int main()
{

	int n;
	cin>>n;

	unsigned long long res=0;
	for(int i=0;i<n;i++){
		unsigned long long c,d;
		cin>>c>>d;

		res+=((unsigned long long)ceil(c/2.0))*d;
		res%=mod;
	}

	cout<<res<<endl;

	return 0;
}