Scanner scan = new Scanner(System.in)

int p = scan.nextInt()
int d = scan.nextInt()
int m = scan.nextInt()
int s = scan.nextInt()

int numGames = 0
int totalCost = 0
int currentCost = p;

while (totalCost < s) {
    if (totalCost + currentCost <= s) {
        numGames++
        totalCost += currentCost
        currentCost -= d
        if (currentCost < m) {
            currentCost = m
        }
    } else {
        break
    }
}

println numGames