// you can also use imports, for example:
// import java.util.*;

// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

class Solution {
    public int solution(int[] A) {
        // write your code in Java SE 8
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        long sum = (long) (A.length + 1) * (long) (A.length + 2) / 2;
        for (int a : A) {
            sum -= a;
        }
        
        return (int) sum;
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        boolean[] array = new boolean[100002];
        for (int a : A) {
            array[a] = true;
        }
        
        for (int i = 1; i <= array.length; i++) {
            if (!array[i]) {
                return i;   
            }
        }
        
        return 100001;   
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        boolean[] array = new boolean[A.length];
        for (int a : A) {
            array[a] = true;
        }
        
        for (int i = 1; i <= array.length; i++) {
            if (!array[i]) {
                return i;   
            }
        }
        
        return 100001;   
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        boolean[] array = new boolean[A.length + 2];
        for (int a : A) {
            array[a] = true;
        }
        
        for (int i = 1; i <= array.length; i++) {
            if (!array[i]) {
                return i;   
            }
        }
        
        return 100001;   
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        boolean[] array = new boolean[A.length + 2];
        for (int a : A) {
            array[a] = true;
        }
        
        for (int i = 1; i <= array.length; i++) {
            if (!array[i]) {
                return i;   
            }
        }
        
        return 100001;   
    }
}

import java.util.*;

class Solution {
    public int solution(int[] A) {
        boolean[] array = new boolean[A.length + 2];
        for (int a : A) {
            array[a] = true;
        }
        
        for (int i = 1; i <= array.length; i++) {
            if (!array[i]) {
                return i;   
            }
        }
        
        return 100001;   
    }
}