#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, k;
  cin >> n >> m >> k;
  vector<int> mas(n);
  for (int i = 0; i < n; i++) cin >> mas[i];
  int ans = INT_MAX / 2;
  for (int i = 0; i < n; i++) {
    if (mas[i] == 0)
      continue;
    else if (mas[i] <= k) {
      ans = min(abs(i - m + 1), ans);
    }
  }
  cout << ans * 10;
  return 0;
}
