import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long sum = 0L;
        long mod = (long)Math.pow(10,9)+7;
        for(long i=0; i<N; i++){
            long C = sc.nextLong();
            long D = sc.nextLong();
            long a = C/2;
            long b = C%2;
            if(b!=0){
                a++;
            }
            sum = sum + a*D;
            sum = sum%mod;
        }
        System.out.println(sum);
    }
}