#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);
        ans += (C+1)/2 * D;
        ans %=1000000007;
    }
    printf("%lld\n", ans);
    return 0;
}