#include <bits/stdc++.h>
  
using namespace std;
  
#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define pb push_back
#define all(r) r.begin(),r.end()
#define rall(r) r.rbegin(),r.rend()
#define fi first
#define se second
  
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
 
const int INF = 1e9;
const ll MOD = 1e9 + 7;
double EPS = 1e-8;

int main(){
	int x, y, n;
	cin >> x >> y >> n;
	vi a(n);
	rep(i, n) cin >> a[i];
	ll sum1 = 0LL, sum2 = 0LL;
	rep(i, n-1) sum1 += a[i];
	rep(i, n) sum2 += a[i];
	cout << (sum1 * y> sum2 * x + EPS? "NO" : "YES") << endl; 

}