#include <bits/stdc++.h>
using namespace std;
inline int read() {
	int x = 0, f = 1;
	char ch = getchar();
	while(!isdigit(ch)) {
		if(ch == '-') f = -1;
		ch = getchar();
	}
	while(isdigit(ch)) {
		x = x * 10 + ch - '0';
		ch = getchar();
	}
	return x * f;
}
const int N = 2e3 + 100;
int n, a[N];
signed main() {
	while(cin >> n) {
		for(int i = 1; i <= n; ++i) a[i] = read();
		int t1 = -1, t2 = -1, flag = 0;
		for(int i = 1; i <= n; ++i) {
			if(t1 < a[i]) t1 = a[i];
			else if(t2 < a[i]) t2 = a[i];
			else {
				flag = 1;
				break;
			}
		}
		if(flag) cout << "No!\n"; 
		else cout << "Yes!\n";
 }
	return 0;
}//fake

100pts,包括P4728