백준 22864번: 피로도 #Python

A, B, C, M = map(int, input().split())

fatigue = 0
work = 0

for _ in range(24):
    if M < A:
        break

    if fatigue + A <= M:
        fatigue += A
        work += B
    else:
        fatigue -= C

        if fatigue < 0:
            fatigue = 0

print(work)