#ifdef Home
#define _GLIBCXX_DEBUG
#endif // Home
#include <bits/stdc++.h>
using namespace std;
typedef long double ld;
struct My{
int x, y, z;
bool operator < (My &b) {
return x == b.x ? (y == b.y ? z < b.z : y < b.y) : x < b.x;
}
};
map < int , map < int, int > > mp;
int get(int x, int y) {
auto it = mp.lower_bound(x);
if(it == mp.begin()) {
return 0;
}
-- it;
auto it2 = it->second.lower_bound(y);
if(it2 == it->second.begin()) {
return 0;
}
-- it2;
return it2->second;
}
int mtx[4040][4040];
main() {
#ifdef Home
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif // Home
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, m, k, mx = 0;
cin >> n;
vector < My > V(n);
for(auto &[x, y, z] : V) {
cin >> x >> y >> z;
mx = max({mx, x, y, z});
}
if(mx <= 4000) {
for(auto &[x, y, z] : V) {
mtx[x][y] = max(mtx[x][y], z);
auto it = mp.find(x);
if(it == mp.end()) {
mp[x];
it = mp.find(x);
}
auto it2 = it->second.find(y);
if(it2 == it->second.end()) {
it->second[y] = z;
} else {
it2->second = min(it2->second, z);
}
}
for(int i = 1; i <= mx; ++ i) {
for(int j = 1; j <= mx; ++j) {
mtx[i][j] = max({mtx[i][j], mtx[i][j - 1], mtx[i - 1][j]});
}
}
mx = 0;
for(auto it = prev(mp.end()); it != mp.begin(); it --) {
int x = it->first;
for(auto &[y, z] : it->second) {
for(auto it2 = prev(it);; it2 --) {
int x2 = it2->first;
if(x2 >= x) {
continue;
}
for(auto &[y2, z2] : it2->second) {
if(y2 <= y) {
continue;
}
k = mtx[x - 1][y2 - 1];
if(k > z && k > z2) {
mx = max(mx, x + y2 + k);
}
}
if(it2 == mp.begin()) {
break;
}
}
}
}
cout << (mx ? mx : -1);
return 0;
}
sort(V.begin(), V.end());
for(int i = 0; i < n; ++ i) {
auto it = mp.find(V[i].x);
if(it == mp.end()) {
mp[V[i].x];
it = mp.find(V[i].x);
}
auto it2 = it->second.find(V[i].y);
if(it2 == it->second.end()) {
it->second[V[i].y] = V[i].z;
} else {
it2->second = max(it2->second, V[i].z);
}
if(i + 1 < n && V[i].x == V[i + 1].x) {
continue;
}
if(it != mp.begin()) {
auto pre_mp = prev(it);
for(auto &[key, val] : pre_mp->second) {
auto it2 = it->second.find(key);
if(it2 == it->second.end()) {
it->second[key] = val;
} else {
it2->second = max(it2->second, val);
}
}
}
mx = 0;
for(auto &[key, val] : it->second) {
mx = max(mx, val);
val = mx;
}
}
/**
for(auto &[x, y, z] : V) {
cout << x << ' ' << y << ' ' << z << '\n';
}
cout << '\n';
for(auto &[key, val] : mp) {
for(auto &[key2, val2] : val) {
cout << key << ' ' << key2 << ' ' << val2 << '\n';
}
}
// */
mx = 0;
for(int i = n; i --> 0;) {
for(int j = i; j --> 0;) {
if(V[i].x > V[j].x && V[j].y > V[i].y) {
k = get(V[i].x, V[j].y);
if(k > V[i].z && k > V[j].z) {
mx = max(mx, V[i].x + V[j].y + k);
}
}
}
}
cout << (mx ? mx : -1);
}
