#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

int main(int argc, char const *argv[]) {
  int n;std::cin >> n;
  vector<ld> a(n);
  ld s = 0, e = 0;
  re(i, n) {
    std::cin >> a[i];
    s += a[i];
  }
  s/=n;
  re(i, n){
    e += (a[i]-s)*(a[i]-s);
  }
  e = sqrt(e/n);
  if(e<1e-8){
    std::cout << 50 << '\n';
    return 0;
  }
  re(i, n){
    a[i] = (10.0*(a[i]-s))/e;
    a[i] += 50.0;
  }
  ll m;std::cin >> m;
  std::cout << (int)(a[m-1]+1e-8) << '\n';
  return 0;
}