Go: package main

import "fmt"

func main() {
	var n int
	fmt.Scanln(&n)
	l, r, max := 0, 63, 0
	for l <= r {
		m := (l + r) / 2
		pow2 := 1 << uint(m)
		if pow2 <= n {
			l = m + 1
			if pow2 > max {
				max = pow2
			}
		} else {
			r = m - 1
		}
	}
	fmt.Println(max)
}

C++: #include<bits/stdc++.h>
#include<vector>
#include<deque>
#include<list>
#define rep(i,n) for(ll i=0;i<n;++i)
#define rrep(i,n) for(int i=n-1;i>=0;--i)
#define yesno(flg) if(flg){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}
#define MAX_N 1002
#define i197 1000000007

using namespace std;

typedef long long ll;
typedef pair<ll,ll> P1;
typedef pair<int,int> Pi;
typedef pair<double,Pi> Pdi;
typedef pair<ll,int>Pli;
typedef pair<P1,ll> P2;
const ll INF=10000000000000000001;
struct edge{int to,cost;};
struct pos{
	int x,y,cost;
};
int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0};
struct Road{double cost;int a,b;};


int main() {

	ll n;
	cin>>n;
	ll ans=2;
	while(ans*2<=n){
		ans*=2;
	}
	cout<<ans<<endl;
	return 0;
}

C++: #include <iostream>
using namespace std;

int main(void){
    int a; cin >> a;
    int j = 2;
    while(1){
        if(a - j * 2 < 0)  break;
        j *= 2;
    }
    cout << j << endl;
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;

int main() {
	long long N, N_ = 1;
	cin >> N;
	while (1) {
		if (N_ * 2 > N) {
			cout << N_ << endl;
			return 0;
		}
		N_ *= 2;
	}
}

C++: #include <stdio.h>
int main(void) {
	int N, i, b = 1;
	scanf("%d", &N);
	for (i = 0; b<=N; i++) {
		b = b * 2;
	}
	if (N%b == 0) {
		printf("%d\n",b);
	}
	else {
		b = b / 2;
		printf("%d\n",b);
	}
	return 0;
}

C++: #include <iostream>
#include <map>
#include <vector>
#include <cmath>
#include <string>
#include <algorithm>
using namespace std;

int main() {
	long long N; cin >> N;
	int ans = 1;
	while (ans * 2 <= N) {
		ans *= 2;
	}
	cout << ans << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
using lint = long long;
constexpr lint mod = 1e9 + 7;
#define all(x) (x).begin(), (x).end()
#define bitcount(n) __builtin_popcountl((lint)(n))
#define fcout cout << fixed << setprecision(15)
#define highest(x) (63 - __builtin_clzl(x))
#define rep(i, n) for(int i = 0; i < int(n); i++)
#define rep2(i, l, r) for(int i = int(l); i < int(r); i++)
#define repr(i, n) for(int i = int(n) - 1; i >= 0; i--)
#define repr2(i, l, r) for(int i = int(r) - 1; i >= int(l); i--)
#define SZ(x) int(x.size())
constexpr int inf9 = 1e9; constexpr lint inf18 = 1e18;
inline void YES(bool condition){ if(condition) cout << "YES" << endl; else cout << "NO" << endl; }
inline void Yes(bool condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
inline void assertNO(bool condition){ if(!condition){ cout << "NO" << endl; exit(0); } }
inline void assertNo(bool condition){ if(!condition){ cout << "No" << endl; exit(0); } }
inline void assertm1(bool condition){ if(!condition){ cout << -1 << endl; exit(0); } }
lint power(lint base, lint exponent, lint module){ if(exponent % 2){ return power(base, exponent - 1, module) * base % module; }else if(exponent){ lint root_ans = power(base, exponent / 2, module); return root_ans * root_ans % module; }else{ return 1; }}
struct position{ int y, x; }; position mv[4] = {{0, -1}, {1, 0}, {0, 1}, {-1, 0}}; double euclidean(position first, position second){ return sqrt((second.x - first.x) * (second.x - first.x) + (second.y - first.y) * (second.y - first.y)); }
template<class T, class U> string to_string(pair<T, U> x){ return to_string(x.first) + "," + to_string(x.second); } string to_string(string x){ return x; }
template<class T> string to_string(complex<T> x){ return to_string(make_pair(x.real(), x.imag())); }
template<class itr> void array_output(itr start, itr goal){ string ans; for(auto i = start; i != goal; i++) cout << (i == start ? "" : " ") << (*i); if(!ans.empty()) ans.pop_back(); cout << ans << endl; }
template<class itr> void cins(itr first, itr last){ for(auto i = first; i != last; i++){ cin >> (*i); } }
template<class T> T gcd(T a, T b){ if(b) return gcd(b, a % b); else return a; }
template<class T> T lcm(T a, T b){ return a / gcd(a, b) * b; }
struct combination{ vector<lint> fact, inv; combination(int sz) : fact(sz + 1), inv(sz + 1){ fact[0] = 1; for(int i = 1; i <= sz; i++){ fact[i] = fact[i - 1] * i % mod; } inv[sz] = power(fact[sz], mod - 2, mod); for(int i = sz - 1; i >= 0; i--){ inv[i] = inv[i + 1] * (i + 1) % mod; } } lint P(int n, int r){ if(r < 0 || n < r) return 0; return (fact[n] * inv[n - r] % mod); } lint C(int p, int q){ if(q < 0 || p < q) return 0; return (fact[p] * inv[q] % mod * inv[p - q] % mod); } };
template<class itr> bool next_sequence(itr first, itr last, int max_bound){ itr now = last; while(now != first){ now--; (*now)++; if((*now) == max_bound){ (*now) = 0; }else{ return true; } } return false; }
template<class itr, class itr2> bool next_sequence2(itr first, itr last, itr2 first2, itr2 last2){ itr now = last; itr2 now2 = last2; while(now != first){ now--, now2--; (*now)++; if((*now) == (*now2)){ (*now) = 0; }else{ return true; } } return false; }
template<class T> bool chmax(T &a, const T &b){ if(a < b){ a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b){ if(b < a){ a = b; return 1; } return 0; }
inline int at(lint i, int j){ return (i >> j) & 1; }
random_device rnd;
bool is_in_board(lint y, lint x, lint H, lint W){ return (0 <= y && y < H && 0 <= x && x < W); }

int main(){
    int N;
    cin >> N;
    int p = 1;
    while(p * 2 <= N){
        p *= 2;
    }
    cout << p << endl;
}

C++: #include <iostream>
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
//using graph = vector<vector<ll>>;


int main() {
	ll n,mem=2;
	cin >> n;
	while (n >= mem) {
		mem = mem * 2;
	}
	cout << mem / 2 << endl;
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

int main() {
	int n, mul;

	cin >> n;
	mul = 1;
	while (mul <= n) {
		mul <<= 1;
	}
	cout << (mul >> 1) << endl;

	return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main() {
	int a;
	int b = 2;
	cin >> a;
	for (;;) {
		b*=2;
		if (b > a) {
			b /= 2;
			break;
		}
	}

	cout << b<<endl;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){
  int N,M;
  M = 1;
  cin >> N;
  while(1){
    if(N > M){
      M = M*2;
    }
    else if(N == M){
      cout << M << endl;
      break;
    }else if (N < M){
      cout << M/2 << endl;
      break;
    }
  }
  
    
}

C++: #include<iostream>
using namespace std;

int main(){
	int n, x=2;
	cin >> n;
	n /= 2;
	
	while(n>=x){x *= 2;}
	cout << x << endl;
	
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int power(int a){
    int rev=1;
    for(int i=0;i<a;i++){
        rev*=2;
    }
    return rev;
}
int main(void){
    int n,ans;
    cin >>n;
    for(int i=1;i<=21;i++){
        if(n<power(i)){
            ans=power(i-1);
            break;
        }
    }
    cout << ans << endl;
}

C++: #include "bits/stdc++.h"

using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    int k = 1;
    while (2 * k <= n) {
        k *= 2;
    }
    cout << k << '\n';
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
  int n;
  cin >> n;
  int now=1;
  while(1){
      if(now>n){
          cout << now/2 << endl;
          return 0;
      }
      now*=2;
  }
}