#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <queue>
#include <bitset>
#include <stack>
#include <functional>

// AtCoder
#include <atcoder/all>
using namespace atcoder;

#ifdef LOCAL
    #define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
    #define eprintf(...)
#endif

#define rep_(i, a_, b_, a, b, ...) for (int i = (a), i##_len = (b); i < i##_len; ++i)
#define rep(i, ...) rep_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define reprev_(i, a_, b_, a, b, ...) for (int i = (b)-1, i##_min = (a); i >= i##_min; --i)
#define reprev(i, ...) reprev_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define all(x) (x).begin(), (x).end()
template <class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template <class T> bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }
#define fls(x) (64 - __builtin_clzll(x))
#define pcnt(x) __builtin_popcountll(x)
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair <int,int> P;
typedef long double ld;

int main (void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll t, x, a, y, b;
    cin >> t >> x >> a >> y >> b;
    
    ll ans = 1e18, cost_b = (max(a * b - t, 0LL) + b - 1) / b;
    while (cost_b >= 0) {
        ll day_b = -cost_b * b;
        if (day_b > t) break;
        chmin(ans, (t - day_b) / a * x + cost_b * y + (t - day_b) % a);
        eprintf("cost_b=%lld day_b=%lld\n", cost_b, day_b);
        --cost_b;
    }
    cout << ans << endl;
    return 0;
}