a, p, s, m = map(int, input().split())


ls = [p for i in range(12)]
for i in range(s,s+m,1):
    ls[i-1] = p*2
cnt = 0
while a > 0:
    for i in ls:
        if a > 0:
            a -= i
            cnt += 1
        else:
            break
print(cnt)