#include <iostream>
using namespace std;
typedef long long LL;
const LL MAX=1e9+7;
int main(int argc, char* argv[])
{
	int N;
	cin>>N;
	LL ans=0;
	int i;
	LL C;
	LL D;
	for (i=0;i<N;i++){
		cin>>C;
		cin>>D;
		if (C==1){
			ans+=D;
		}else{
			if (C%2==0){
				ans+=(C/2)*D;
			}else{
				ans+=(C/2+1)*D;
			}
		}
		ans%=MAX;
	}
	cout<<ans<<endl;
	return 0;
}