#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define rrep2(ri,x,n) for(int ri = (int)(n-1); ri >= (int)(x); ri--)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

int main(){
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i, n) cin >> a.at(i);
  bool ans = false, st = false;
  rep(i, n){
    if(a.at(i) > (i+1)) ans = true;
    else if(a.at(i) == (i+1)){
      if(i != 0){
        if(st == false) st = true;
        else ans = true;
      }
    }else if(a.at(i) < i){
      if(!(st == true && a.at(i) == 0))ans = true;
    }
  }
  if(ans == false) cout << "Yes" << endl;
  else cout << "No" << endl;
  return 0;
}