#include <bits/stdc++.h>
int main() {
  int i, n, m, k, min = 1000000009, t, temp;
  scanf("%d %d %d", &n, &m, &k);
  for (i = 1; i <= n; i++) {
    scanf("%d", &t);
    if (t > 0 && t <= k) {
      temp = abs(m - i);
      if (temp < min) min = temp;
    }
  }
  printf("%d\n", (min * 10));
  return 0;
}
