#include <bits/stdc++.h>
using namespace std;
int n, m, k, i, dis = 10000000, temp, a[1000];
int main() {
  cin >> n >> m >> k;
  for (i = 0; i < n; ++i) cin >> a[i];
  for (i = 0; i < n; ++i) {
    if (a[i] != 0 && a[i] <= k) {
      if (m <= i)
        temp = (i - m + 1) * 10;
      else
        temp = (m - i - 1) * 10;
      if (dis > temp) dis = temp;
    }
  }
  cout << dis;
  return 0;
}
