#include<bits/stdc++.h>
main(){
    int N,m = 1000000007;
    scanf("%d",&N);
    long long sum = 0;
    for(int i = 0;i < N;i++){
        long long C,D;
        scanf("%lld%lld",&C,&D);
        sum += (C+1)/2%m*D%m;
        sum %= m;
    }
    printf("%lld\n",sum);
}