#!/bin/ruby

def howManyGames(p, d, m, s)
    cost = p
    num = 0
    while s >= cost
        num += 1
        s -= cost
        cost -= d
        cost < m ? cost = m : cost
    end
    return num
end

p, d, m, s = gets.strip.split(' ')
p = p.to_i
d = d.to_i
m = m.to_i
s = s.to_i
answer = howManyGames(p, d, m, s)
puts answer