#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)

using ll = long long;
using P = std::tuple<int,int>;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

int A[100];

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int X, Y;
    std::cin >> X >> Y;

    int N;
    std::cin >> N;

    for(int i=0;i<N;++i){
        std::cin >> A[i];
    }

    bool missed = false;
    for(int i=0;i+1<N;++i){
        if(Y * A[i] > X * A[i+1]){missed = true;}        
    }

    const string YESNO[2] = {"NO", "YES"};
    std::cout << YESNO[!missed] << std::endl;
}