#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, k, current, mir;
  cin >> n >> m >> k;
  vector<int> arr;
  for (int i = 0; i < n; i++) {
    cin >> current;
    if (current <= k) {
      arr.push_back(current);
    } else
      arr.push_back(0);
  }
  int dist, minus = 2000, price, minusP = 200;
  for (int i = 0; i < n; i++) {
    if (arr.at(i) != 0) {
      dist = abs(i - (m - 1));
      price = arr.at(i);
      if (dist < minus) {
        minus = dist;
      }
    }
  }
  cout << minus * 10 << endl;
  return 0;
}
