#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, k;
  int buy = -1;
  scanf("%d %d %d", &n, &m, &k);
  int meters = 10 * m;
  for (int i = 1; i <= n; ++i) {
    int c;
    scanf("%d", &c);
    meters = (i <= m) ? meters - 10 : meters + 10;
    if (c != 0 && c <= k && (buy == -1 || buy > meters)) {
      buy = meters;
    }
  }
  printf("%d\n", buy);
  return 0;
}
