#include<bits/stdc++.h>
using namespace std;
int main()
{
    int N,M,X,T,D;
    cin>>N>>M>>X>>T>>D;
    if(M<X)
    {
        cout<<T-(X-M)*D;
    }
    else
    {
        cout<<T;
    }   
    return 0;
}