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

if B == C:
    exit(print(0))

# B - C 人に A個ずつ渡す
ans = D
X = D
for i in range(2, (B - C)*A + 1):
    if i%10 == 0:
        if E <= X:
            cost = X - E
        else:
            cost = X
    else:
        cost = X
    
    ans += cost
    X = cost
print(ans)