#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1e5+7;
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x=0) :
            val(x), left(NULL), right(NULL) {
    }
};
int TreeDepth(TreeNode* pRoot){
    if(pRoot!=NULL)return max(TreeDepth(pRoot->left),TreeDepth(pRoot->right))+1;
    return 0;
}
void dfs(TreeNode* pRoot){    //建树
    scanf("%d",&pRoot->val);
    int flag;
    scanf("%d",&flag);
    if(flag==-1){
        TreeNode *left=new TreeNode;
        pRoot->left=left;
        dfs(pRoot->left);
    }
    else if(flag==-2){
        TreeNode *left=new TreeNode;
        pRoot->right=left;
        dfs(pRoot->right);
    }
    else if(flag==-3){
        TreeNode *left=new TreeNode;
        TreeNode *right=new TreeNode;
        pRoot->right=right;
        pRoot->left=left;
        dfs(pRoot->left);
        dfs(pRoot->right);
    }
    else if(flag==-4)return;
}
int main(){
    TreeNode root;
    int x;
    dfs(&root);
    cout<<TreeDepth(&root)<<endl;
    return 0;
}