6C

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <set>
#include <stack>
#include <queue>
#include <deque>
using namespace std;

#define TASK "bstsimple"

struct node {
    int t;
    node *left, *right;
    node(int tt) {
        t = tt;
        left = NULL;
        right = NULL;
    }
};

node *root, *last;

node *find(node *x, int t) {
    if (x == NULL || x->t == t) {
        return x;
    }
    if (t < x->t) {
        return find(x->left, t);
    }
    return find(x->right, t);
}

node *min(node *x) {
    if (x->left == NULL) {
        return x;
    }
    return min(x->left);
}

node *max(node *x) {
    if (x->right == NULL) {
        return x;
    }
    return max(x->right);
}

node *prev(node *x, int t) {
    if (x == NULL || x->t == t) {
        if (x != NULL && x->left != NULL) {
            return max(x->left);
        }
        return last;
    }
    if (t < x->t) {
        return prev(x->left, t);
    }
    last = x;
    return prev(x->right, t);
}

node *next(node *x, int t) {
    if (x == NULL || x->t == t) {
        if (x != NULL && x->right != NULL) {
            return min(x->right);
        }
        return last;
    }
    if (t < x->t) {
    last = x;
        return next(x->left, t);
    }
    return next(x->right, t);
}

node *ins(node *x, int t) {
    if (x == NULL) {
        return new node(t);
    }
    if (t < x->t) {
        x->left = ins(x->left, t);
    }
    else if (t > x->t) {
        x->right = ins(x->right, t);
    }
    return x;
}

node *del(node *x, int t) {
    if (x == NULL) {
        return x;
    }
    if (t < x->t) {
        x->left = del(x->left, t);
    }
    else if (t > x->t) {
        x->right = del(x->right, t);
    }
    else if (x->left != NULL && x->right != NULL) {
        x->t = min(x->right)->t;
        x->right = del(x->right, x->t);
    }
    else if (x->left != NULL) {
        x = x->left;
    }
    else {
        x = x->right;
    }
    return x;
}

int main() {

#ifdef _DEBUG
    freopen("debug.in", "r", stdin);
    freopen("debug.out", "w", stdout);
#else
    freopen(TASK".in", "r", stdin);
    freopen(TASK".out", "w", stdout);
#endif // _DEBUG

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    string s;
    int x;
    node *t;
    while (cin >> s) {
        cin >> x;
        switch (s[0]) {
        case 'i': root = ins(root, x); break;
        case 'd': root = del(root, x); break;
        case 'e': cout << (find(root, x) == NULL ? "false\n" : "true\n"); break;
        case 'n': last = NULL; t = next(root, x); if (t == NULL) cout << "none"; else cout << t->t; cout << "\n"; break;
        case 'p': last = NULL; t = prev(root, x); if (t == NULL) cout << "none"; else cout << t->t; cout << "\n"; break;
        }
    }

    return 0;
}