D cf

#include <bits/stdc++.h>

using namespace std;

// Prioridade
typedef long long   ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pii> vpi;

#define F first
#define S second
#define PB push_back
#define MP make_pair
#define REP(i,a,b) for(int i = a; i < (int)(b); i++)
#define INF 0x3f3f3f3f
#define INFLL 0x3f3f3f3f3f3f3f3f
#define all(x) x.begin(),x.end()
#define MOD 1000000007
#define endl '\n'
#define mdc(a, b) (__gcd((a), (b)))
#define mmc(a, b) (((a)/__gcd(a, b)) * b)
#define W(x) cerr << "\033[31m"<<  #x << " = " << x << "\033[0m" << endl;
// fim da Prioridade
ll d,k,a,b,t;
ll work(ll mid){
	if((mid/k) *k == mid && mid != 0){
		return mid*a + ((mid)/k - 1) * t+(d-mid)*b;
	}
	return mid*a + ((mid/k) * t) + (d-mid)*b;
}
int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	cin >> d >> k >> a >> b >> t;
	ll lo = 0, hi = d,mid1, mid2;

	while(hi - lo > 300){
		mid1 = (2*lo+hi)/3 ;
		mid2 = (lo+2*hi)/3;

		//cout << work(mid1) << " " << work(mid2) << endl;
		if(work(mid1) > work(mid2)){
			lo = mid1;
		}else{
			hi = mid2;
		}
	}
	ll ans = 1LL<<62;
	for(ll i = lo;i <= hi;i++){
		ans = min(ans,work(i));

	}
	cout << ans << endl;
	return 0;
}