#include <bits/stdc++.h>
using namespace std;
int main() {
  double n, m, a, b;
  cin >> n >> m >> a >> b;
  double s = n / m;
  long long int s1 = floor(s) * m;
  long long int s2 = ceil(s) * m;
  long long int a1 = (n - s1) * b;
  long long int a2 = (s2 - n) * a;
  cout << (min(a1, a2));
}
