N,M,P,Q = map(int,input().split())
now = 1
mod = 12
ans = 0
s =set()
for _ in range(Q):
    s.add((P + _) % mod)
while N:
    ans += 1
    if now in s:
        N = max(0,N - 2 * M)
    else:
        N = max(0,N - M)
    now = (now + 1) % mod
print(ans)