#include <iostream>
using namespace std;
int main(){
	int n;	cin>>n;
	long long int c,d,count=0;
	for(int i=0;i<n;i++){
		cin>>c>>d;
		c=(c+1)/2;
		count+=c*d;
		count%=1000000007;
	}
	cout<<count<<endl;
	return 0;
}