import java.util.Arrays;

public class PermMissingElem {

public static void main(String[] args) {

int[] A = {2,1,3,4};

Arrays.sort(A);

for(int i = 0; i <= A.length; i++) {

if(i == A.length) {

System.out.println(i + 1);

break;

}

if (i + 1 != A[i]) {

System.out.println(i + 1);

break;

}

}

}

}