import std.stdio, std.algorithm, std.array, std.conv, std.typecons;

alias Set = bool[3 * 10^^5];

void main() {
	readln;
	auto P = readln.split.to!(ulong[]);
	P = [0UL] ~ P;
	auto N = P.length-1;
	
	auto set = new bool[N+1];
	foreach (p; P) {
		set[p] = true;
	}
	
	auto ans = new bool[N+1];
	foreach (i; 1 .. N+1) if (!set[i]){
		if (P[i] != 0 && P[P[i]] != 0) ans[P[P[i]]] = true;
	}
	
	writeln(ans.count(true));
}