#include <stdio.h>

int main(void){
    int i, N;
    long long C, D, ans = 0;
    scanf("%d", &N);
    for(i=0;i<N;i++){
        scanf("%lld %lld", &C, &D);
        if(C%2==0){
            ans += C/2 * D;
        }else{
            ans += (C/2 + 1) * D;
        }
    }
    if(ans>=1000000007){
        printf("%lld\n", ans%1000000007);
    }else{
        printf("%lld\n", ans);
    }
    return 0;
}