#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-f;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
int buf[30];
inline void print(int x,char ch=' '){
	if(x<0) putchar('-'),x=-x;
	int tot=0;
	do{
		buf[++tot]=x%10;
		x/=10;
	}while(x);
	for(int i=tot;i;i--)
		putchar(buf[i]+'0');
	putchar(ch);
}
const int MAXN=1e5+5;
int n,m,root;
vector<int> e[MAXN];
struct node{
	int siz,dep,son,dist;
}a[MAXN];
void dfs1(int x,int dep){
	a[x].siz=1,a[x].dep=dep;
	for(int to:e[x]){
		dfs1(to,dep+1);
		a[x].siz+=a[to].siz;
		if(a[to].dist>a[a[x].son].dist)	
			a[x].son=to;
	}
	a[x].dist=a[a[x].son].dist+1;
}
set<int> s[MAXN];
set<int>::iterator it;
int *f[MAXN],g[MAXN],*now=g,tot;
struct info{
	int u,v,x;
	info(int a=0,int b=0,int c=0){
		u=a,v=b,x=c;
	}
}b[MAXN<<1];
int num;
void dfs2(int x){
	s[f[x][0]=++tot].insert(x);
	if(!a[x].son) return ;
	f[a[x].son]=f[x]+1;
	dfs2(a[x].son);
	for(int to:e[x]){
		if(to==a[x].son) continue;
		f[to]=now,now+=a[to].dist;
		dfs2(to);
		for(int i=0;i<a[to].dist;i++)
			for(int y:s[f[to][i]]) s[f[x][i+1]].insert(y);
	}
	for(int to:e[x]){
		if(to==a[x].son) continue;
		for(int i=0;i<a[to].dist;i++){
			for(int y:s[f[to][i]]){
				it=s[f[x][i+1]].lower_bound(y);
				if(it!=s[f[x][i+1]].begin()){
					it--;
					b[++num]=info(*it,y,i+1);
					it++;
				}
				if(it!=s[f[x][i+1]].end()){
					it++;
					b[++num]=info(y,*it,i+1);
					it--;
				}
			}
		}
	}
}
signed main(){
	n=read(),m=read();
	for(int i=1;i<=n;i++){
		int x=read();
		if(x==0) root=i;
		else e[x].push_back(i);
	}
	dfs1(root,1);
	f[root]=now,now+=a[root].dist;
	dfs2(root);
	cout<<num;
	return 0;
}