#include<iostream>

using namespace std;

#define MOD (1000000000+7)

int main(){

	long long N,C,D,ans=0;

	cin>>N;
	for(int i=0;i<N;i++){
		cin>>C>>D;
		ans+=D;
		C--;
		ans+=(long long)(C/2)*D;
		ans%=MOD;
	}

	cout<<ans<<endl;
}