#include <iostream>
#include <vector>
using namespace std;

int main(void) {
int x, y;
int n;
cin >> x >> y >> n;
vector<int> a(n);
for (int i = 0; i < n; ++i) {cin>>a[i];}
bool ok = 1;
for (int i = 0; i < n - 1; ++i) {
ok &= a[i + 1] * x >= a[i] * y;
}
cout << (ok ? "YES" : "NO") << endl;
}