-`using namespace std;`: this saves lots of tedious typing of`std::` before all the standard library functions and objects. However, a blanket namespace import like this can cause name clashes, so don't name your variables or functions something common like`find` or anything from[this list](https://en.cppreference.com/w/cpp/symbol_index).

-`#include <bits/stdc++.h>`: this is a catch-all implementation-defined header in g++ that avoids having a list of dozens of includes like`#include <vector>`,`#include <iostream>`,`#include <string>`, etc. It should work on any CP judge site, but it is not a standard header.

-`#define int long long`: some people define`int` to always be (at least) 64-bit to avoid overflow issues, since most CP problems use numbers that fit in a 64-bit integer. However, be aware of unexpected issues:

- C++ requires`main` to be a function returning`int` and not`long long`, so use`signed main` as a workaround.

- Function calls like`min(x, 0)` may complain that`0` is type`int`.

- May require twice as much memory than`int` and make the program slower, which may be important in extremely time-critical code.

- Otherwise you can use`typedef long long ll` or use the appropriate fixed-width integer types like`int64_t`.