A, B, C, D, E = map(int, input().split())
K = A * (B - C)
KAI = 0

for i in range(1, K + 1):
    if i % 10 != 0:
        KAI += D
    elif i % 10 == 0 and E <= D:
        D -= E
        KAI += D
    elif i % 10 == 0 and E > D:
        KAI += D


print(KAI)