import java.util.Scanner;

public class Example {

    private static int k;
    private static int n;
    private static int[] array;
    private static int sum = 0;

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        k = scanner.nextInt();
        n = scanner.nextInt();
        if(k>=1 && n>=1 && n<=100){
            Scanner scan = new Scanner(System.in);
            array = new int[n];
            for (int i = 0; i < n; i++) {
                array[i] = scan.nextInt();
                if(array[i]>=0 && array[i]<=100){
                    if((array[i]-k) >= 0){
                        sum+=(array[i]-k);
                    }else if(Math.abs(array[i]-k)<sum){
                        sum=sum+array[i]-k;
                    }else sum = 0;
                }
            }
            System.out.println(sum);
        }
    }

}