Uva 514

#include<cstdio>
#include<cmath>
#include<cctype>
#include<iostream>
#include<vector>
#include<cstring>
#include<algorithm>
#include<map>
#include<set>
#include<cstddef>
#include<sstream>
#include<cstdlib>
#include<stack>
#include<queue>

using namespace std;

const int MAXN = 1000 + 10;

int n, target[MAXN];

int main() {
    while(cin >> n) {
        stack<int> s;
        int A = 1, B = 1;
        for(int i = 1; i <= n; i++)
            cin >> target[i];//初始化火车
        int ok = 1;
        while(B <= n) {
            if(A == target[B]) { A++; B++; }
            else if(!s.empty() && s.top() == target[B]) { 
                s.pop(); B++; }
            else if(A <= n) s.push(A++);
            else { ok = 0; break; }
        }
        cout << (ok ? "Yes" : "No") << endl;
    }
    return 0;
}