#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cassert>
#include <functional>
#include <algorithm>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
using namespace std;
using llong = long long;

llong n, k, m;
llong sum;

int main() {
    cin >> n >> k >> m;
    for (int i = 0; i < n - 1; i++) {
        llong a;
        cin >> a;
        sum += a;
    }

    if ((n * m) - sum > k) {
        cout << -1 << endl;
    }
    else {
        cout << max(0ll, (n * m) - sum) << endl;
    }

    return 0;
}

#include<bits/stdc++.h>
#define G getchar();getchar();
using namespace std;
const double eps = 0.0000001;
void solve()
{
    double a,b,c;
    cin>>a>>b>>c;
    double d=sqrt(b*b+c*c);
    int i=0;
    while(d>2*a)//d==2*a
    {
        d-=a;
        i++;
    }
    if(d==a)//d==a
    {
        i+=1;
    }
    else    i+=2;
    cout<<i;
    G
}
int main()
{
    solve();
    return 0;
}