#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    long long c=1,t,p,d,m,mx,s;
    cin>>p>>d>>m>>mx;
    s = p;
    t = p;
    if(p > mx){
        cout<<0;
        return 0;
    }
    while(1)
    {
        t -= d;
        if(t <= m)
        {
            t = m;
        }
        s += t;
        if(s > mx){
            break;
        }
        c++;
    }
    cout<<c;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}