import java.util.Scanner;
public class MEGA {

    public static void main(String[] args) {
        Scanner sc = new Scanner (System.in);
        int capacity = sc.nextInt();
        int minutes = sc.nextInt();
        int stoppedcars = 0;
        for (int i=1; i<=minutes; i++) {
            int thisminutecars = sc.nextInt();
            if (thisminutecars > capacity) stoppedcars = thisminutecars - capacity;
            if (thisminutecars < capacity) stoppedcars = stoppedcars - (capacity - thisminutecars);
        }
        if (stoppedcars < 0) stoppedcars = 0;
        System.out.println(stoppedcars);


    }

}

Edited by author 17.09.2012 17:51

Step through in the debugger and see if the changes to stoppedcars makes sense to you.  Do you properly handle cars left over from previous minutes?