#include "hack.h" #include <bits/stdc++.h> using namespace std; using ll = long long; using vi = vector<ll>; int hack(){ int l = 1, r = 5e5; while(l < r) { int mid = (l+r)/2; vi v; if(l != 1) v.push_back(1); for(int i=l; i<=mid; ++i) v.push_back(i); int x = collisions(v); if(x) r = mid; else l = mid + 1; } return r-1; }