#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, m, k;
  cin >> n >> m >> k;
  vector<long long> a(n + 1, 0);
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
  }
  long long result(10e8);
  for (int i = 1; i <= n; i++) {
    if (a[i] != 0) {
      if (a[i] <= k and abs(m - i - 1) * 10 <= result) {
        result = (abs(m - i)) * 10;
      }
    }
  }
  cout << result;
}
