WA2个点0分求调，玄1关

#include<bits/stdc++.h>
using namespace std;
int n,a[300000],f[300000][60],ans;
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)
    cin>>a[i],f[i][a[i]]=i+1;
    for(int j=2;j<=56;j++)
    for(int i=1;i<=n;i++){
        if(f[i][j]==0)f[i][j]=f[f[i][j-1]][j-1];
        if(f[i][j]>0)ans=max(ans,j);
    }
    cout<<ans;
}