#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

int main(){
    int n;cin>>n;
    vector<int> A(n);
    int sm = 0;
    for(int i = 0; n > i; i++){
        cin>>A[i];
        sm += A[i];
    }
    int m;cin>>m;m--;
    vector<double> B(n);
    double sm2 = 0;
    for(int i = 0; n > i; i++){
        B[i] =(A[i]-(sm/(double)n))*(A[i]-(sm/(double)n)); 
        sm2 += B[i];
    }
    double c = sqrt(sm2/n);
    if(c == 0){
        cout << 50 << endl;
    }else{
        cout << (int)(50+(A[m]-(sm/(double)n))*10/c) << endl;
    }
}