#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T gcd(T a, T b) {
  return (b) == 0 ? (a) : gcd((b), ((a) % (b)));
}
template <class T>
inline T lcm(T a, T b) {
  return ((a) / gcd((a), (b)) * (b));
}
template <class T>
inline T BigMod(T Base, T power, T M = 1000000007) {
  if (power == 0) return 1;
  if (power & 1)
    return ((Base % M) * (BigMod(Base, power - 1, M) % M)) % M;
  else {
    T y = BigMod(Base, power / 2, M) % M;
    return (y * y) % M;
  }
}
template <class T>
inline T ModInv(T A, T M = 1000000007) {
  return BigMod(A, M - 2, M);
}
int fx[] = {-1, +0, +1, +0, +1, +1, -1, -1, +0};
int fy[] = {+0, -1, +0, +1, +1, -1, +1, -1, +0};
int day[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int arr[500005];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  int mx = 0;
  for (int i = 1; i <= n; i++) {
    cin >> arr[i];
    mx = max(mx, arr[i]);
  }
  int flag = 0;
  stack<int> st;
  for (int i = 1; i <= n; i++) {
    if (st.empty())
      st.push(arr[i]);
    else if (st.top() > arr[i])
      st.push(arr[i]);
    else if (st.top() < arr[i]) {
      flag = 1;
      break;
    } else {
      st.pop();
    }
  }
  if (flag) {
    cout << "NO\n";
    return 0;
  }
  if (st.size() == 0 || st.size() == 1 && st.top() == mx)
    cout << "YES\n";
  else
    cout << "NO\n";
  return 0;
}
