import java.util.*;
import java.lang.*;
import java.io.*;

class Main
{
	public static void main (String[] args)
	{
	    int[] array = { 1,2,3,5,6,7,8,9,10 };
	    int len=10;
	    int expected_sum=len*(len+1)/2;
	    int real_sum=0;
	    for(int i:array){
	        real_sum+=i;
	    }
	    System.out.println("The missing number is: "+(expected_sum-real_sum));
	}
}