#include using namespace std; #define int long long int #define endl "\n" signed main(){ ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int n;cin>>n; vector p(n+1),idg(n+1,0),s(n+1,0); for(int i=1;i<=n;i++){ cin>>p[i]; if(p[i] != 0)idg[p[i]]++; } for(int i=1;i<=n;i++){ if(idg[i]!=0)continue; int x = p[i]; if(x==0)continue; int y = p[x]; if(y==0)continue; s[y] = 1; } int ans=0; for(int i=1;i<=n;i++){ ans += s[i]; } cout<