#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 2000000000000000001


int main(){
	
	long long t,x,a,y,b;
	cin>>t>>x>>a>>y>>b;
	long long ans = Inf64;
	for(long long i=0;i<=20000000;i++){
		long long cx = -i;
		long long ca = i;
		ca *= y;
		cx *= b;
		if(cx > t)continue;
		long long d = t - cx;
		ca += (d/a) * x;
		ca += d%a;
		ans = min(ans,ca);
		
	}
	cout<<ans<<endl;
	
	return 0;
}