#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,k,m,sum(0),avg,ans(-1);
  cin >> n >> k >> m;
  for(int i = 0;i<n-1;i++){
    cin >> avg;
    sum += avg;
  }
  avg = sum/n;
  if(m <= avg){
    ans = 0;
  }else if((m*n-sum) <= k){
    ans = m*n - sum;
  }
  cout << ans << endl;
}
#include <stdio.h>
#include<iostream>
#include <string>
#include <string.h>
#include <vector>
#include <cmath>
#include <algorithm>
#include <queue>
#include <climits>
#include <set>
#include <unordered_map>
#include <map>
#include <stack>
#include <unordered_set>
#define hash hassh
using namespace std;
int main() {
    int T=1;
    //cin>>T;
    while(T--) {
        int a,b,k;
        cin>>a>>b>>k;
        k*=1000;
        if(k<a){
            puts("UNSATISFIABLE");
            continue;
        }
        int t=k/a;
        if(t*b<k){
            puts("UNSATISFIABLE");
            continue;
        }
        swap(a,b);
        printf("%d %d\n",k/a+(k%a>0),k/b);
    }
    return 0;
}
//注意检查边界
//注意考虑某些数组/向量可能为空 可能引起错误
//注意各种边界是0还是1
//注意少加不必要的限制条件 避免出错
//不要把前期题想得太难，尝试找简单结论