#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int X, Y;
	cin >> X >> Y;
	int N;
	cin >> N;
	vector<int> A(N);
	REP(i, N) scanf("%d", &A[i]);
	puts([&]() -> bool {
		REP(i, N - 1) {
			// A[i]/X * Y > A[i+1]
			if (A[i] * Y > A[i + 1] * X) return false;
		}
		return true;
	}() ? "YES": "NO");
}