a,b,c,d,e=map(int,input().split())
n=b-c*a
f=0
x=d
for j in range(n):
    for i in range(1,a+1):
        if i<2:
            f+=d
        elif i%10!=0:
            f+=X
        elif e>x:
            f+=X
        else:
            x=x-e
            f+=x
print(f)