#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define printVec(v) printf("{"); for (const auto& i : v) { std::cout << i << ", "; } printf("}\n");
#define degreeToRadian(deg) (((deg)/360)*2*M_PI)
#define radianTodegree(rad) (((rad)/2/M_PI)*360)
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
using namespace std;
using P = pair<int,int>;
using ll = long long;
const ll INF = 1LL<<60;
const int MOD = 1e9 + 7;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

//cin.tie(0);ios::sync_with_stdio(false);
//cout << fixed << setprecision(15) << y << endl;
int main() {
  int N;
  cin >> N;
  vector<int> a(N + 1);
  for (int i = 1; i <= N; i++) cin >> a[i];

  bool ok = false;
  if (N < 2) ok = true;
  
  for (int i = 2; i <= N; i++) {
    if (a[i] + 1 == i) continue;
    if (a[i] == i) {
      ok = true;
      for (int j = i + 1; j <= N; j++) {
	if (a[j] == 0) continue;
	ok = false;
      }
      break;
    } else {
      ok = false;
    }
  }

  if (ok) cout << "Yes" << endl;
  else cout << "No" << endl;
  return 0;
}