#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <sstream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

int main() {
    int32_t x, y, n;
    cin >> x >> y >> n;
    vector<int32_t> as(n + 1);
    for (auto i = 0; i < n; ++i) {
        cin >> as[i];
    }
    as[n] = numeric_limits<int32_t>::max() / 1000;
    bool ans = true;
    for (auto i = 0; i < n; ++i) {
        if (as[i] * y > as[i + 1] * x) {
            ans = false;
            break;
        }
    }
    cout << (ans ? "YES" : "NO") << endl;
    return 0;
}