#include <bits/stdc++.h>
using namespace std;

int main()
{
	int a, b, c, d, e;
	cin >> a >> b >> c >> d >> e;


	int ans = a - b;
	for( int i = 0; i <= c; i++ ) {
		ans = max( ans, (a + i * d) - (b + i * e) );
	}
	
	cout << ans << endl;
}