let n = readLine()!.split(separator: " ").map{Int($0)!}
var (a,b,c,d,e) = (n[0],n[1],n[2],n[3],n[4])
var m = a * (b - c)
var s = 0
for i in 0...m{
    if (i + 1) % 10 > 0{
        s += d
    }else if d < e{
        s += d
    }else{
        s += d - e
        d -= e
    }
}
print(s)