546B. Soldier and Badges

import java.io.PrintStream;
import java.util.Arrays;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;


public class B546 {

    static void run(){
        Scanner in = new Scanner(System.in);
        PrintStream out = System.out;
        int n = in.nextInt();
        int[] a = new int[n];
        Set set = new TreeSet();
        for(int i=0;i<n;i++){
            a[i] = in.nextInt();
        }
        Arrays.sort(a);
        int count = 0;
        for(int i=0;i<n;i++){
            while(set.contains(a[i])){
                a[i]++;
                count++;
            }
            set.add(a[i]);
        }
        out.println(count);
    }
    public static void main(String[] args){
        run();
    }
}

def B546():
    n = int(raw_input())
    a = map(int, raw_input().split())
    
    d = {} # dict
    count = 0 
    for i in range(n):
        while str(a[i]) in d :
            a[i]+=1
            count+=1 
        d[str(a[i])] = 1
    #print d 
    print count 
    
    
if __name__==‘__main__‘:
    B546()