#include<bits/stdc++.h>
#define ll long long
#define pii pair<int, int>
#define pip pair<int, pair<int,int> >
#define mp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
#define sd(n) scanf("%d",&n)
#define sld(n) scanf("%lld",&n)
//#define MOD 1000000007
#define F first
#define S second
using namespace std;

int dx[] = {-1,0,1,0};
int dy[] = {0,1,0,-1};
const int MAX = int(1e5)+1;
const int MOD = int(1e9)+7;




int main() {

    int p,d,m;
    ll s;
    sd(p);sd(d);sd(m);
    scanf("%lld",&s);
    
    vector<ll> price;
    
    int i=0;
    ll sum = p;
    for(;i<MAX;i++){
        price.pb(sum);
        sum-=d;
        if(sum<=m){
            break;
        }
    }
    for(;i<MAX;i++){
        price.pb(m);
    }
    
    for(int i=1; i<MAX; i++){
        price[i]+=price[i-1];
        //cout<<price[i]<<" ";
    }
    
    int ans_ind = lower_bound(price.begin(), price.end(), s)-price.begin();
        if(price[ans_ind]==s)
            cout<<ans_ind+1;
        else
            cout<<ans_ind;
        //cout<<endl;
        //cout<<price[ans_ind]<<endl;
    
    
    
    return 0;
}