#include <iostream>
#include <string>
#include <assert.h>
using namespace std;

int a[100];

int main(void){
    
    int x,y,n;
    cin >> x >> y >> n;
    
    assert(x >= 1 && x <= 100);
    assert(y >= 1 && y <= 100);
    assert(n >= 1 && n <= 80);
    
    for(int i = 0; i < n; i++)
        cin >> a[i];
    
    bool f = true;  
    
    for(int i = 0; i < n-1; i++){
        
        
        assert(a[i] < a[i+1]);
        assert(0 < a[i] && a[i] <= 100000);
    
        if((a[i+1]) * x < ( a[i] * y ) ){
            f = false;
        }
    }
    
    if(f)
    cout << "YES" << endl;
    else
    cout << "NO" << endl;
    
}