//author : RUTVIK KOTHARI
//DA-IICT
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define mod 1000000007
ll power(ll _a,ll _b){ll _r=1;while(_b){if(_b%2==1)_r=(_r*_a);_b/=2;_a=(_a*_a);}return _r;}
ll add(ll a,ll b,ll m=mod){ll x=a+b;while(x>=m)x-=m;return x;}
ll sub(ll a,ll b,ll m=mod){ll x=a-b;while(x<0)x+=m;return x;}
ll mul(ll a,ll b,ll m=mod){ll x=a*b;x%=m;return x;}
ll gcd(ll a,ll b){while(a&&b)a>b?a%=b:b%=a;return a+b;}
ll lcm(ll a,ll b){return (max(a,b)/gcd(a,b))*min(a,b);}
int main()
{
    ios_base::sync_with_stdio(false);
    ll m,p,d,s,i;
    cin>>p>>d>>m>>s;
    ll count=0,c=0;
    i=p;
    while(1)
    {
        //if(i<=m || s<=0)
        //{c=1;break;}
        if(s<=0)
            break;
        if(s-i<0)
            break;
        else
        {
            count++;
            s-=i;
            i=i-d;
            if((i)<=m)
            {c=1;break;}
        }
    }
    //cout<<count;
    if(c==1)
    {count+=(s/m);}
    cout<<count;
    return 0;
}