#include <bits/stdc++.h>
using namespace std;
int n, m, k, ans;
int a[111];
int main() {
  cin >> n >> m >> k;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= n; i++) {
    if (m + i >= 1 && m + i <= n) {
      if (a[m + i] != 0 && a[m + i] <= k) {
        ans = i;
        break;
      }
    }
    if (m - i >= 1 && m - i <= n) {
      if (a[m - i] != 0 && a[m - i] <= k) {
        ans = i;
        break;
      }
    }
  }
  cout << ans * 10;
  return 0;
}
