#include <iostream>
#include <cmath>
int main(void){
    int N,K,M,l,i;
  	double SUM = 0.0;
    double j,k;
  	int *A;
  
	std::cin >> N >> K >> M;
  
  	A = new int[N-2];
  	i = 0;
  	while(std::cin>>l){
        A[i] = l;
        i++;
        SUM = SUM + l;
    }

  	j = M * N - SUM; 
  
  	if (j < 0){
    	j = 0;	
    } 
  	
  	if(j > K){
    	j = -1;
    }
  
    std::cout << std::ceil(j);
  	
  
	return 0;
}
#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<math.h>
using namespace std;

int main() {
	long double a, b, r, u, l;
	unsigned long long c = 0;
	long n, m;

	
	cin >> a >> b >> r;
    r += 1E-14;
	n = ceil((a - r));
	m = floor(a + r);
	for (long i = n; i <= m ; i++) {
		u = sqrt((r * r) - (i - a)*(i - a));
		u = floor(b + u);
		l = sqrt((r * r) - (i - a) * (i - a));
		l = ceil(b - l);
		c += u - l + 1;
	}
	cout << c;
	return 0;
}