//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  int A, B, C, D; cin >> A >> B >> C >> D;
  int start = A;
  
  while(true){
    bool flag = true;
    
    if(A == 0){
      flag = false;
    }
    if(B < C){
      flag = false;
    }
    if(D < 1+C){
      flag = false;
    }
    
    if(!flag){
      printl(start-A);
      return 0;
    }
    
    D -= (1+C);
    A--;
    B -= C;
  }
}