#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp> // Common file
//#include <ext/pb_ds/tree_policy.hpp> // Including seg_tree_order_statistics_node_update
#include <stdio.h>
#include <cassert>
using namespace std;
//using namespace __gnu_pbds;
typedef long long lo;
typedef pair<lo,lo> ll;//pair
typedef vector<lo> vl;  //vector of long
typedef vector<ll > vll;   //vector of pair
typedef priority_queue<lo>p_q;
typedef vector< vl > vvl;  //vector of vectors
#define X first
#define Y second
#define mp(a,b) make_pair((a),(b))
#define REP(a,b) for(lo i=(a);i<(lo)b;i++)//no need to declare variable i
#define REPE(a,b,c,d) REP(a,b)for(lo j=(c);j<(lo)d;j++)//no need to declare vaiables i,j
#define REPV(a,b,c) for((a)=b;(a)<(c);(a)++)//a is the variable
#define IREP(a,b) for(lo i=(a);i>=(b);i--)
#define IREPV(a,b,c) for((a)=b;(a)>=(c);(a)--)
#define all(v) (v).begin(),(v).end()
#define TRV(a) for(auto it : a)
#define INF 200100
#define MOD 1000000007
#define M 1000000007
#define CHECK_BIT(var,pos) ((var) & (1<<(pos)))
#define pb(a) push_back((a))
/*order statistic tree
typedef
tree<
  lo,
    null_type,
  less_equal<lo>,
  rb_tree_tag,
  // This policy updates nodes' metadata for order statistics.
  tree_order_statistics_node_update>
ordered_set;*/

/*#define gc getchar_unlocked
#define pc putchar_unlocked
inline void sprlo( lo a){
    lo i=0;
    char S[20];
    if(a==0)pc('0');
    if(a<0){
        pc('-');
        a*=-1;
    }
    while(a>0){
        S[i++]=a%10+'0';
        a=a/10;
    }
    --i;
    while(i>=0)
    pc(S[i--]);
    pc(' ');
}
inline void lprlo( lo a){
    lo i=0;
    char S[20];
    if(a==0)pc('0');
    while(a>0){
        S[i++]=a%10+'0';
        a=a/10;
    }
    --i;
    while(i>=0)
    pc(S[i--]);
    pc('\n');
}
inline lo uscan(){
    lo n=0;
    char c=gc();
    while(c<'0'||c>'9')c=gc();
    while(c<='9'&&c>='0'){
	    n=n*10+c-'0';
	    c=gc();
	}
    return n;
}*/
template<typename T> ostream& operator<< ( ostream &o,vector<T> v ) {
    if ( v.size() >0 )o<<v[0];
    for ( unsigned   i=1; i<v.size(); i++ )o<<" "<<v[i];
    return o<<endl;
}
template<typename U,typename V> ostream& operator<< ( ostream &o,pair<U,V> p ) {
    return o<<"("<<p.first<<", "<<p.second<<") ";
}
template<typename T> istream& operator>> ( istream &in,vector<T> &v ) {
    for ( unsigned   i=0; i<v.size(); i++ )in>>v[i];
    return in;
}
template<typename T> istream& operator>> ( istream &in,pair <T,T> &p ) {
    in>>p.X;
    in>>p.Y;
    return in;
}
lo dig(lo n){
    lo x=0;
    while(n>0){
        n/=10;
        x++;
    }
    return x;
}
int main(){
    std::ios::sync_with_stdio(false);
	lo p,d,m,s;
	cin>>p>>d>>m>>s;
	lo ans=0;
    lo sum=0;
	while(sum<=s){
        sum+=p;
        //cout<<p<<endl;
        if(p>m)p-=d;
        if(p<m)p=m;
        ans++;
	}
    cout<<ans-1;
	return 0;
}