#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
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(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

ll T,X,A,Y,B;


void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>T>>X>>A>>Y>>B;
	
	ll ret=1LL<<60;
	for(i=0;i<=30000000;i++) {
		ll a=1LL*A*i;
		ll b=X*i;
		
		if(a>=1000000000) continue;
		if(a>=T) {
			ll c=(a-T+B-1)/B;
			a-=B*c;
			b+=Y*c;
		}
		assert(a<=T);
		b+=T-a;
		ret=min(ret,b);
	}
	cout<<ret<<endl;
	
	
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}