#include <bits/stdc++.h>
using namespace std;
int main() {
  int m, n, k, l = 9999, j = 9999, s, i;
  cin >> n >> m >> k;
  int a[n + 3];
  for (i = 1; i <= n; i++) cin >> a[i];
  for (i = m + 1; i <= n; i++) {
    if (a[i] != 0 && a[i] <= k) {
      l = (i - m);
      break;
    }
  }
  for (i = m - 1; i >= 1; i--) {
    if (a[i] != 0 && a[i] <= k) {
      j = (m - i);
      break;
    }
  }
  s = min(j, l);
  cout << s * 10;
}
