//---------------------------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#pragma hdrstop

//---------------------------------------------------------------------------
int N;
int *M;

#pragma argsused
void leeEntrada()
{
        int i;
        FILE *in = fopen( "input.txt", "r" );
        fscanf( in, "%d\n", &N );
        M = new int[N];
        for( i = 0; i < N; i++ )
                fscanf( in, "%d", &M[i] );
        fclose( in );
}
/*
void hazEntradaRandom()
{
        int i;
        N = random( 10000 ) + 1;
        M = new int[N];
        for( i = 0; i < N; i++ )
                M[i] = random( N-1 );
}
*/
int calculaMayor()
{
        int i, tmp, count;
        for( i = N-1; i >= 0; i-- )
        {
                tmp = M[i];
                count = 0;
                while( tmp != 0 && count < N+1 )
                {
                        tmp = M[tmp];
                        count++;
                }
                if( tmp == 0 )
                        return i;
        }
        return -1;
}

void escribeSolucion( int best )
{
        FILE *out = fopen( "output.txt", "w" );
        fprintf( out, "%d", best );
        fclose( out );
}
/*
void escribeEntrada()
{
        int i;
        FILE *in = fopen( "input.txt", "w" );
        fprintf( in, "%d\n", N );
        for( i = 0; i < N-1; i++ )
                fprintf( in, "%d ", M[i] );
        fprintf( in, "%d", M[N-1] );
        fclose( in );
}
*/
int main(int argc, char* argv[])
{
        //randomize();
        //hazEntradaRandom();
        leeEntrada();
        int best = calculaMayor();
        //if( best > 0 )
        //        escribeEntrada();
        escribeSolucion( best );
        delete[] M;
        return 0;
}
//---------------------------------------------------------------------------