#include "testlib.h"
#include <bits/stdc++.h>

using namespace std;

int main(){
  registerValidation();
  long long t=inf.readLong(-10000000ll,10000000ll);inf.readEoln();
  ensuref(t!=0,"t==0");
  long long x=inf.readLong(1ll,10000000ll);inf.readSpace();
  long long a=inf.readLong(x+1,10000000ll);inf.readEoln();
  long long y=inf.readLong(1ll,10000000ll);inf.readSpace();
  long long b=inf.readLong(1ll,10000000ll);inf.readEoln();
  inf.readEof();

  long long cent=25'000'000;
  vector<long long> dp(50'000'000,8e18);
  for(int i=cent;i<5e7;i++){dp[i]=i-cent;}
  for(int i=50'000'000-1;i>=b;i--){
    dp[i-b]=min(dp[i-b],dp[i]+y);
  }
  for(int i=0;i<50'000'000-a;i++){
    dp[i+a]=min(dp[i+a],dp[i]+x);
  }
  cout << dp[cent+t] << "\n";
  return 0;
}