a, b, c, d = map(int, input().split())
ls = [b for i in range(12)]
for i in range(c,c+d,1):
    ls[i-1] = b*2
ans = 0
while a > 0:
    for i in ls:
        if a > 0:
            a -= i
            ans += 1
        else:
            break
print(ans)