import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long[] c = new long[n];
        long[] d = new long[n];
        for(int i=0; i<n; i++) {
            c[i] = in.nextLong();
            d[i] = in.nextLong();
        }

        long ans = 0;
        for(int i=0; i<n; i++) {
            long t = (c[i] - 1) / 2 + 1;
            ans += t * d[i];
        }

        System.out.println(ans % 1000000007);

    }
}