a,b,c,d,e = map(int,input().split())

need = a*(b-c)

ans = 0
x = d
for i in range(1,need+1):
    if i%10:
        ans += x
    else:
        if e <= x:
            ans += x-e
            x = x-e
        else:
            ans += x
print(ans)