#include<bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
typedef long long LL;
LL X,Y;
LL N;
LL A[100001];
int main(){
	cin>>X>>Y>>N;
	REP(i,N){
	    cin>>A[i];
	}
	REP(i,N-1){
	    if(A[i+1]*X<A[i]*Y){
	       cout<<"NO"<<endl;
	       return 0;
	    }
	}
        cout<<"YES"<<endl;
	return(0);
}