package java_core;
import java.util.Scanner;

public class LoopsAssignment3 {


    public static void main(String args[]){
                Scanner sc = new Scanner(System.in);
        System.out.println("Kinldy input 3 numbers: ");

    int a = sc.nextInt();
    int b = sc.nextInt();
    int c = sc.nextInt();
    if (a==7){
        System.out.println(b*c);
    }
    else if (b==7){
        System.out.println(c);
    }
    else{
        System.out.println(-1);
    }
    }



    }