# Enter your code here. Read input from STDIN. Print output to STDOUT

inputs = input().strip().split(" ")
startPrice = int(inputs[0])
difference = int(inputs[1])
endPrice = int(inputs[2])
totalMoney = int(inputs[3])

answer = 0
currPrice = startPrice

while (totalMoney >= 0):
    answer += 1
    #print(currPrice)
    totalMoney -= currPrice
    if (currPrice - difference >= endPrice):
        currPrice -= difference
    else:
        currPrice = endPrice
        
print(max(answer - 1, 0))