#include <stdio.h>
#include <stdlib.h>
#define N 20000
int max(int a, int b) { return a > b ? a : b; }
int *ej[N], eo[N];
void append(int i, int j) {
int o = eo[i]++;
if (o >= 2 && (o & o - 1) == 0)
ej[i] = (int *) realloc(ej[i], o * 2 * sizeof *ej[i]);
ej[i][o] = j;
}
int dd[N];
void dfs1(int i, int d) {
int o;
dd[i] = d;
for (o = eo[i]; o--; ) {
int j = ej[i][o];
dfs1(j, d + 1);
}
}
int d_;
void dfs2(int i, int d) {
int o;
d_ = max(d_, d);
for (o = eo[i]; o--; ) {
int j = ej[i][o];
dfs2(j, d + 1);
}
}
int main() {
static int pp[N], qu[N];
static char visited[N];
int n, cnt, h, i, j, o;
scanf("%d", &n);
for (i = 0; i < n; i++)
ej[i] = (int *) malloc(2 * sizeof *ej[i]);
for (i = 0; i < n; i++) {
scanf("%d", &pp[i]);
if (pp[i] != -1)
append(pp[i], i);
}
for (i = 0; i < n; i++)
if (pp[i] == -1)
dfs1(i, 1);
i = 0, cnt = 0;
while (i >= 0 && !visited[i])
qu[cnt++] = i, visited[i] = 1, i = pp[i];
if (i >= 0) {
d_ = 0;
for (i = 0; i < n; i++)
d_ = max(d_, dd[i]);
printf("%d\n", cnt + d_);
} else {
d_ = cnt;
for (i = 0; i < n; i++)
if (pp[i] == -1 && i != qu[cnt - 1])
dfs2(i, cnt + 1);
for (h = cnt - 1; h > 0; h--) {
i = qu[h];
for (o = eo[i]; o--; ) {
j = ej[i][o];
if (j != qu[h - 1])
dfs2(j, cnt + 1);
}
}
printf("%d\n", d_);
}
return 0;
}
