import java.util.*;
import java.math.*;
import java.io.*;
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		BigInteger bi = new BigInteger("0");
		int n = sc.nextInt();
		BigInteger sum = new BigInteger("0");
		for(int i = 0; i < n; i++) {
			BigInteger c = sc.nextBigInteger();
			BigInteger d = sc.nextBigInteger();
			BigInteger e = new BigInteger("0");
			e = c.divide(new BigInteger("2")).add(new BigInteger("1"));
			if(c.mod(new BigInteger("2")).equals(new BigInteger("0"))) {
				e = e.subtract(new BigInteger("1"));
			}
			sum = sum.add(e.multiply(d));
			sum = sum.mod(new BigInteger("1000000007"));
		}
		System.out.println(sum.toString());
		
	}
 }