#include <iostream>
 
using namespace std;
 
int main() {
    int n;
    while (cin >> n) {
        int seq[n], num = 1, stack[n], stacksize = 0;
 
        for (int i = 0; i < n; ++i) {
            cin >> seq[i];
            stack[i] = 0;
        }
 
        for (int i = 0; i < n; ++i) {
            while (stacksize == 0 || stack[stacksize - 1] < seq[i])
                stack[stacksize++] = num++;
            if (stack[stacksize - 1] == seq[i])
                stack[stacksize--] = 0;
        }
 
        stacksize == 0 ? cout << "YES" : cout << "NO";
    }
    return 0;
}

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