#include <atcoder/all>
#include <bits/stdc++.h>

using namespace std;

// #define DISABLE_PRINT

#if defined(ENABLE_PRINT) && !defined(DISABLE_PRINT)

#define P(...) fprintf(stderr, __VA_ARGS__)
#define LP fprintf(stderr, "L: %d\n", __LINE__)

#else

#define P(...) ((void)0)
#define LP ((void)0)

#endif

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define ALL(x) x.begin(), x.end()

using ll = long long;
using ull = unsigned long long;

const int INF = 1100100100;
const ll INFLL = 1100100100100100100;

int main() {
    ll A, B, C, D, E;
    cin >> A >> B >> C >> D >> E;
    auto ans = A - B;
    rep(i, C) {
        A += D;
        B += E;
        ans = max(ans, A - B);
    }
    cout << ans << endl;
    return 0;
}