#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, k, pos = 105;
  cin >> n >> m >> k;
  for (int i = 1; i <= n; i++) {
    int h;
    cin >> h;
    if (h != 0) {
      if (h <= k) {
        int dist = abs(m - i);
        if (dist < pos) pos = dist;
      }
    }
    if (pos == 1) break;
  }
  cout << pos * 10 << "\n";
  return 0;
}
