int howManyGames(int p, int d, int m, int s) {
    int result = 0;
    while( s >= p){
        s -= p;
        p = max(m, p-d);
        result++;
    }
    return result;
}

int howManyGames(int p, int d, int m, int s){
    if( s < p) return 0;
    return howManyGames( max(m, p-d), d, m, s - p) + 1;
}

int howManyGames(int p, int d, int m, int s) {
    int n = 1 + (p - m) / d;
    int total = (p + p - (n - 1) * d) * n / 2;
    if(total <= s) {
        return n + (s - total) / m;
    }
    else 
        return 0;
        // this return need to be computed properly
}

def howManyGames(p, d, m, s):
    # Return the number of games you can buy
     
    count = 0 
    i = p
    
    while s - i >= 0:
        count += 1
        s -= i
        i = max(m, i - d )
                   
    return count 

module Main where

solve p d m s =
    let seqH = takeWhile (>= m) $ iterate (subtract d) p
        seqT = repeat m
        sums = scanl1 (+) $ seqH ++ seqT
     in length $ takeWhile (<= s) sums

main :: IO ()
main = do
    [p, d, m, s] <- fmap (map read . words) getLine
    print $ solve p d m s

def howManyGames(p, d, m, s):
    ans=0
    while s>=p:
        s-=p
        ans+=1
        p-=d
        if p<m:
            p=m
    return ans

oreo=a=p
  q=0
  while True:
    if a<=m:
      a=m
    else:
      a-=d
    if a<=m:
      a=m
    if oreo==s:
      q+=1
      return q
      break 
    elif oreo>s:
      oreo-=a
      return q
      break
    elif oreo<s:
      q+=1
      oreo+=a