#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>
#include <limits>

static const int MOD = 998244353;
using ll = long long;
using uint = unsigned;
using ull = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    a -= b; d -= e;
    cout << max(a, a+c*d) << "\n";
    return 0;
}