#ifdef __APPLE__
#include "bits:stdc++.h"
#define debug(A,N) PLLD(A,N)
#else
#include <bits/stdc++.h>
#define debug(A,n) ;
#endif
#define REPP(i,j,n) for(LL i = j;i < n; ++i)
#define REP(i,n) for(LL i = 0;i < n; ++i)
using namespace std;

typedef long long LL;
typedef pair<LL,LL> PLL;

auto scan = []{static LL a;scanf("%lld",&a);return a;};

#define MAXN 1000
PLL A[MAXN];

int main(){
  LL p = scan(), d = scan() , m = scan(), s = scan() ,ans = 0;
  while(p <= s){
    s -= p;
    ++ans;
    p = max(m, p - d);
  }
  printf("%lld\n",ans);
}