#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N = 155;
const int INF = 2e9;

int dp[N][N];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    freopen("bridge.in", "r", stdin);
    freopen("bridge.out", "w", stdout);

    int x, a, y, b, l;
    cin >> x >> a >> y >> b >> l;

    int lo = min(a,b) + 1, hi = 50000;

    while (lo < hi)
    {
        int mid = (lo + hi) / 2;

        bool good = 1;

        fill_n(&dp[0][0], N * N, INF);

        dp[0][0] = 0;

        for (int i = 1; i <= l; ++i)
        {
            for (int j = 0; j <= x; ++j)
            {
                for (int kx = 0; kx <= j; ++kx)
                {
                    int ky = max(0, (mid - kx * a + b - 1) / b);
                    dp[i][j] = min(dp[i][j], dp[i - 1][j - kx] + ky);
                }
            }
        }

        good = 0;
        for (int i = 0; i <= x; ++i)
            good |= (dp[l][i] <= y);

        if (good)
            lo = mid + 1;
        else
            hi = mid;

    }

    cout << lo - 1 << "\n";

    return 0;
}