//start of jonathanirvings' template v2.0.0 (BETA)
#define jonathan using
#define ganteng namespace
#define banget std
#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <deque>
#include <string>
#include <string.h>
#include <vector>
#include <stack>
#include <queue>
#include <math.h>
#include <stdlib.h>
#include <map>
#include <set>
#include <time.h>
#include <bitset>
#include <list>
jonathan ganteng banget;
typedef long long LL;
typedef pair<int,int> pii;
typedef pair<pii,pii> ppi;
typedef pair<LL,LL> pll;
typedef pair<string,string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<LL> vl;
typedef vector<vl> vvl;
typedef vector<string> vstr;
typedef vector<char> vc;
double EPS = 1e-9;
int INF = 2000000000;
long long INFF = 8000000000000000000LL;
double PI = acos(-1);
int dirx[8] = {-1,0,0,1,-1,-1,1,1};
int diry[8] = {0,1,-1,0,-1,1,-1,1};
#ifdef TESTING
#define DEBUG fprintf(stderr,"====TESTING====\n")
#define VALUE(x) cerr << "The value of " << #x << " is " << x << endl
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define DEBUG
#define VALUE(x)
#define debug(...)
#endif
#define FOR(a,b,c) for (int (a)=(b);(a)<(c);++(a))
#define FORN(a,b,c) for (int (a)=(b);(a)<=(c);++(a))
#define FORD(a,b,c) for (int (a)=(b);(a)>=(c);--(a))
#define FORSQ(a,b,c) for (int (a)=(b);(a)*(a)<=(c);++(a))
#define FORL(a,b,c) for (LL (a)=(b);(a)<=(c);++(a))
#define FORLSQ(a,b,c) for (int (a)=(b);(LL)(a)*(LL)(a)<=(c);++(a))
#define FORC(a,b,c) for (char (a)=(b);(a)<=(c);++(a))
#define REP(i,n) FOR(i,0,n)
#define REPN(i,n) FORN(i,1,n)
#define REPD(i,n) FORD(i,n,1)
#define MAX(a,b) a = max(a,b)
#define MIN(a,b) a = min(a,b)
#define SQR(x) ((x) * (x))
#define RESET(a,b) memset(a,b,sizeof(a))
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ALL(v) v.begin(),v.end()
#define ALLA(arr,sz) arr,arr+sz
#define SIZE(v) (int)v.size()
#define SORT(v) sort(ALL(v))
#define REVERSE(v) reverse(ALL(v))
#define SORTA(arr,sz) sort(ALLA(arr,sz))
#define REVERSEA(arr,sz) reverse(ALLA(arr,sz))
#define PERMUTE next_permutation
#define TC(t) while(t--)
#define READ(n,data) {scanf("%d",&n); REPN(i,n) scanf("%d",&data[i]);}
inline string IntToString(int a){
char x[100];
sprintf(x,"%d",a); string s = x;
return s;
}
inline int StringToInt(string a){
char x[100]; int res;
strcpy(x,a.c_str()); sscanf(x,"%d",&res);
return res;
}
inline string GetString(void){
char x[1000005];
scanf("%s",x); string s = x;
return s;
}
inline string uppercase(string s){
int n = SIZE(s);
REP(i,n) if (s[i] >= 'a' && s[i] <= 'z') s[i] = s[i] - 'a' + 'A';
return s;
}
inline string lowercase(string s){
int n = SIZE(s);
REP(i,n) if (s[i] >= 'A' && s[i] <= 'Z') s[i] = s[i] - 'A' + 'a';
return s;
}
inline void OPEN (string s) {
freopen ((s + ".in").c_str (), "r", stdin);
freopen ((s + ".out").c_str (), "w", stdout);
}
//end of jonathanirvings' template v2.0.0 (BETA)
int n,m;
int parent[100005];
vi child[100005];
int dp[100005];
int risan;
priority_queue<int> pq;
inline void dfs(int now,int take)
{
int sz = SIZE(child[now]);
dp[now] = 1;
REP(i,sz) dfs(child[now][i],take);
while (!pq.empty()) pq.pop();
REP(i,sz) pq.push(dp[child[now][i]]);
REP(i,take)
{
if (pq.empty()) break;
dp[now] += pq.top();
pq.pop();
}
}
bool bisa(int x)
{
dfs(0,x);
return (dp[0] >= m);
}
int main()
{
scanf("%d %d",&n,&m);
FOR(i,1,n)
{
scanf("%d",&parent[i]);
--parent[i];
child[parent[i]].pb(i);
}
int L = 0, R = n, risan = -1;
while (L <= R)
{
int M = (L + R) >> 1;
if (bisa(M))
{
risan = M;
R = M - 1;
} else L = M + 1;
}
printf("%d\n",risan);
return 0;
}
