#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define mk make_pair
#define pp pair<int,int>
#define inf 1e9
using namespace std;
int siev[1000005];
int phi[1000005];
 
inline void Scan_f(int &a){char c = 0;while(c<33)c = getc(stdin);a = 0;while(c>33){a = a*10 + c - '0';c = getc(stdin);}}
void sieve(){for(int i=2;i<=1e6;i++){if(siev[i]==0){for(int j=i;j<=1e6;j+=i)siev[j]=i,phi[j]=phi[j]*(i-1)/i;}}}
ll gcd(ll a,ll b){if(a<b)swap(a,b);while(b!=0){ll temp=b;b=a%b;a=temp;}return a;}
ll power(ll x, ll y, ll z){if (y == 0)return 1;ll p = power(x, y/2,z) % z;p = (p * p) % z;return (y%2 == 0)? p : (x * p) % z;}
ll modInverse(int a,int m){return power(a, phi[m]-1,m);}
 
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
    /*for(int i=1;i<=1e6;i++)
    phi[i]=i;
    phi[0]=0;
    sieve();*/
    ll p,d,m,s;
    cin>>p>>d>>m>>s;

    ll l=p,cnt=0,sum=0;
    while(l>m&&s-l>0)
    {
    	cnt++;
    	sum+=l;
    	s-=l;
    	l=l-d;
    }

    ll v=0;

    if(s>0&&l<=m)
    v=s/m;

    cout<<cnt+v<<"\n";

 
    return 0;
}