function sub(n, x, y, a) {
    for (let i = 0; i < n - 1; i++) {
        const p1 = parseInt(a[i]);
        const p2 = parseInt(a[i + 1]);
        if (y * p1 > p2 * x) {
            return "NO";
        }
    }
    return "YES";
}
function Main(input) {
    const src = input.split("\n");
    const tmp = src[0].split(" ");
    const x = parseInt(tmp[0]);
    const y = parseInt(tmp[1]);
    const n = parseInt(src[1]);
    const a = src[2].split(" ");
    console.log(sub(n, x, y, a));
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));