#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <valarray>
#include <vector>

#define N 1000
#define MOD 1000000007
#define pe(str) return cout<<(str)<<endl,0
#define px(str) {cout<<(str)<<endl;exit(0);}
#define re(i,n) for(int i=0;i<(n);i++)
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define fe(i,n,f) for_each(i,n,f)
#define bw(a,b,c) (((a)<=(b))&&((b)<=(c)))
#define double long double
using namespace std;

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

int main(void){
	ll x,y;
	ll n;
	cin>>x>>y>>n;
	ll a[n];
	re(i,n)cin>>a[i];
	ll k=a[0];
	rep(i,1,n){
		// double t=(double)(k+a[i])/(double)y;
		if((k+a[i])*x<k*y)pe("NO");
		k+=a[i];
	}
	pe("YES");

	return 0;
}