#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M, K;
  scanf("%d%d%d", &N, &M, &K);
  int *Arr = new int[N + 1];
  int Tmp = INT_MAX;
  int Sol = INT_MAX;
  for (int i = 1; i <= N; i++) {
    scanf("%d", &Arr[i]);
  }
  for (int i = 1; i <= N; i++) {
    if (Arr[i] != 0 && Arr[i] <= K) {
      Tmp = abs((M * 10) - (i * 10));
      Sol = min(Sol, Tmp);
    }
  }
  printf("%d", Sol);
  return 0;
}
