import java.util.*;

public class Solution {

public int missingNumber(int[] nums) {

Arrays.sort(nums);

if(nums[0] != 0)

return 0;

if(nums.length == 1){

if(nums[0] != 0)

return 0;

return 1;

}

int number = 0;

for(int i = 0; i < nums.length -1; i++){

if(nums[i] != (nums[i+1] -1)){

return number+1;

}

number++;

}

if(number != 0)

return nums.length;

return number;

}

}