#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
 
int main()
{
	int n;
	ll c,k,sum=0;
	cin>>n;
	for(int i=0;i<n;i++)
	{
		cin>>c>>k;
		if(c%2)sum+=(c/2+1)*k;
		else sum+=(c/2)*k;
		sum%=1000000007;
	}
    cout<<sum<<endl;
    return 0;
}