N, M, P, Q = map(int, input().split())
current_month = 1
current_leaves = N
answer = 0
end_month_storm = P + Q - 1

while current_leaves > 0:
    if P <= current_month <= end_month_storm:
        # Windy season
        remaining_storm = end_month_storm - current_month + 1
        storm_reduce = remaining_storm * 2 * M
        if current_leaves <= storm_reduce:
            needed = (current_leaves + 2 * M - 1) // (2 * M)
            answer += needed
            break
        else:
            current_leaves -= storm_reduce
            answer += remaining_storm
            current_month = end_month_storm + 1
            current_month = current_month % 12
            if current_month == 0:
                current_month = 12
    else:
        # Regular season
        if current_month < P:
            months_until_storm = P - current_month
        else:
            months_until_storm = (12 - current_month) + P
        normal_reduce = months_until_storm * M
        if current_leaves <= normal_reduce:
            needed = (current_leaves + M - 1) // M
            answer += needed
            break
        else:
            current_leaves -= normal_reduce
            answer += months_until_storm
            current_month += months_until_storm
            current_month = current_month % 12
            if current_month == 0:
                current_month = 12

print(answer)