#include <stdio.h>

#define MOD 1000000007

int main(){
    int N, i;
    long long int C, D, cnt = 0;

    scanf("%d\n", &N);
    for(i = 0; i < N; i++){
        scanf("%lld %lld\n", &C, &D);
        if(C%2 == 0){
            cnt += C/2%MOD*D%MOD;
        }else{
            cnt += (C/2 + 1)%MOD*D%MOD;
        }
    }

    printf("%lld\n", cnt);

    return 0;
}