#include <bits/stdc++.h>
using namespace std;
int n, m, k, a, res = 1e9;
int main() {
  cin >> n >> m >> k;
  for (int i = 1; i <= n; i++) {
    cin >> a;
    if (a && a <= k) res = min(res, abs(m - i) * 10);
  }
  cout << res;
}
