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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int p,d,m,s;
    cin>>p>>d>>m>>s;
    vector<int> v;
    for(int i=p;i>m;i-=d)
        {
            v.push_back(i);
        }
    cout<<v.size();
}