#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(ll i=0;i<n;++i)
#define ocut cout
#define ouct cout
#define itn int

struct Union{
  vector<ll> par;
  Union(ll a){
  par=vector<ll>(a,-1);
  }
  ll find(ll a){
    if(par[a]<0){
      return a;
    }
    else{
      return par[a]=find(par[a]);
    }
  }
  bool same(ll a,ll b){
    return (find(a)==find(b));
  }
  ll size(ll a){
    return -par[find(a)];
  }
  void unite(ll a,ll b){
    ll c=find(a),d=find(b);
    if(c==d)
      return;
    if(size(c)<size(d)){
      swap(c,d);
    }
    par[c]+=par[d];
    par[d]=c;
  }
};

int main(){
  int n;
  cin >> n;
  int a[n];
  rep(i,n){
    cin >> a[i];
  }
  int o;
  int ans=0;
  rep(i,n){
    if(a[i]==i+1){
      o=a[i];
      a[i]=a[j];
      a[j]=o;
      ans++;
    }
  }
  cout << ans;
}