#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, k, a, b;
  cin >> n >> k >> a >> b;
  if (k == 1) {
    cout << (n - 1) * a << endl;
    return 0;
  }
  long long ans = 0;
  while (n != 1) {
    if (n >= k) {
      long long md = n % k;
      ans += md * a;
      n -= md;
      long long prev = n;
      long long curr = n / k;
      ans += min(a * (prev - curr), b);
      n /= k;
    } else if (n < k) {
      ans += (n - 1) * a;
      break;
    }
  }
  cout << ans << endl;
  return 0;
}
