#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int uang;
  int girl;
  int numbers[100000];
  int ans = 0;
  cin >> n;
  cin >> girl;
  cin >> uang;
  int minnumber = 1000000000;
  for (int i = 1; i <= n; i++) {
    cin >> numbers[i];
    if (uang - numbers[i] >= 0 && numbers[i] != 0)
      if (abs(i - girl) * 10 < minnumber) {
        minnumber = abs(i - girl) * 10;
      }
  }
  cout << minnumber << endl;
}
