#include <bits/stdc++.h>
using namespace std;
int d, ans = 2000000, a[105];
int main() {
  int n, m;
  scanf("%d%d%d", &n, &m, &d);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) {
    if (a[i] == 0)
      continue;
    else if (a[i] > d)
      continue;
    else
      ans = min(ans, abs(i - m) * 10);
  }
  printf("%d", ans);
  return 0;
}
