#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e9, MAX = 100100, mod = 1000000007;
signed main() {
  long long n, k, A, B;
  cin >> n >> k >> A >> B;
  long long ans = 0;
  if (k == 1)
    cout << (n - 1) * A;
  else {
    while (n != 1) {
      if (n < k) {
        ans = ans + (n - 1) * A;
        n = 1;
      } else if (n % k != 0) {
        ans = ans + (n % k) * A;
        n = n - n % k;
      } else {
        long long nis = n / k;
        ans += min(B, (n - nis) * A);
        n = n / k;
      }
    }
    cout << ans;
  }
}
