#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <math.h>
#define REP(i, n) for (ll i = 0; i < n; i++)
#define REP1(i, n) for (ll i = 1; i <= n; i++)
#define RREP(i, n) for (ll i = n - 1; i >= 0; i--)
#define RREP1(i, n) for (ll i = n; i >= 1; i--)
#define FOR(i, a, b, c) for (ll i = a; i <= b; i += c)
#define RFOR(i, a, b, c) for (ll i = a; i >= b; i -= c)
#define MAX(a, b) (a > b ? a : b)
#define MIN(a, b) (a < b ? a : b)
#define INF 1145141919
typedef long long ll;

int main() {
    int x, y;
    scanf("%d %d", &x, &y);
    int n;
    scanf("%d", &n);
    int a[80];
    REP(i, n) scanf("%d", &a[i]);
    
    x *= 1000; y *= 1000;

    REP(i, n - 1) {
        if (y * a[i] > a[i + 1] * x) {
            puts("NO");
            return 0;
        }
    }
    puts("YES");
    return 0;
}