import std.stdio, std.string, std.conv, std.algorithm;
import std.range, std.array, std.math, std.typecons;

immutable int inf = 10^^9 + 7;

int x, y;
int n;
int[] a;

void main() {
    scan(x, y);
    scan(n);
    a = readln.split.to!(int[]);

    foreach (i ; 0 .. n - 1) {
        if (a[i] * y > x * a[i + 1]) {
            writeln("NO");
            return;
        }
    }

    "YES".writeln;
}


void scan(T...)(ref T args) {
    auto line = readln.split;
    foreach (ref arg ; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}