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>
using namespace std;
int main(){
  int N;
  cin >> N;
  int n = 1;
  while (n * 2 <= N){
    n *= 2;
  }
  cout << n << endl;
}

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

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

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

#define REP(i,num) for(int i=0;i<(num);++i)
#define LOOP(i) while(i--)
#define ALL(c) c.begin(),c.end()
#define PRINTALL(c) for(auto pitr=c.begin();pitr!=c.end();++pitr){cout<<*pitr;if(next(pitr,1)!=c.end())cout<<' ';}cout<<endl;
#define PAIRCOMP(c,comp) [](const pair<ll,ll>& lhs,const pair<ll,ll>& rhs){return lhs.c comp rhs.c;}

using namespace std;
using ll = long long;

constexpr ll atcoder_mod = 1e9+7;

template<typename T=int>
T in(){T x; cin >> x; return (x);}
template<typename T=int,typename C=vector<T>>
C vecin(int N){C x(N);REP(i,N){x[i]=in<T>();}return move(x);}

void vout(){cout << endl;}
template<typename Head,typename... Tail>
void vout(Head&& h,Tail&&... t){cout << ' ' << h;vout(forward<Tail>(t)...);}
void out(){cout << endl;}
template<typename Head,typename... Tail>
void out(Head&& h,Tail&&... t){cout << h;vout(forward<Tail>(t)...);}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);

	int N=in();
	int V=1;
	while(N/2){
		V<<=1;
		N>>=1;
	}
	out(V);
	return 0;
}

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

int main(){
    int N;
    cin >> N;

    int ans = 1;
    while(N >= (ans << 1)) ans <<= 1;
    cout << ans << endl;
}

C++: #include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i,n) for (int i=0;i<(int)(n);i++)
#define codefor int test;scanf("%d",&test);while(test--)
#define yn(ans) if(ans)printf("Yes\n");else printf("No\n")
#define YN(ans) if(ans)printf("YES\n");else printf("NO\n")
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD=1000000007;
//入力系
void scan(int& a){scanf("%d",&a);}
void scan(long long& a){scanf("%lld",&a);}
template<class T> void scan(T& a){cin>>a;}
template<class T> void scan(vector<T>& vec){for(auto&& it:vec)scan(it);}
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail){scan(head);in(tail...);}
//出力系
void print(const int& a){printf("%d",a);}
void print(const long long& a){printf("%lld",a);}
void print(const double& a){printf("%.15lf",a);}
template<class T> void print(const T& a){cout<<a;}
template<class T> void print(const vector<T>& vec){if(vec.empty())return;print(vec[0]);for(auto it=vec.begin();++it!= vec.end();){putchar(' ');print(*it);}}
void out(){putchar('\n');}
template<class T> void out(const T& t){print(t);putchar('\n');}
template <class Head, class... Tail> void out(const Head& head,const Tail&... tail){print(head);putchar(' ');out(tail...);}
//デバッグ系
template<class T> void dprint(const T& a){cerr<<a;}
template<class T> void dprint(const vector<T>& vec){if(vec.empty())return;cerr<<vec[0];for(auto it=vec.begin();++it!= vec.end();){cerr<<" "<<*it;}}
void debug(){cerr<<endl;}
template<class T> void debug(const T& t){dprint(t);cerr<<endl;}
template <class Head, class... Tail> void debug(const Head& head, const Tail&... tail){dprint(head);cerr<<" ";debug(tail...);}

int main(){
    int d=1,n;
    in(n);
    while(d<=n){
        d*=2;
    }
    out(d/2);
}

C++: #include<deque>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#include<set>
#include<cmath>
#include<tuple>
#include<string>
#include<chrono>
#include<functional>
#include<iterator>
#include<random>
#include<unordered_set>
#include<array>
#include<map>
#include<iomanip>
#include<assert.h>
#include<list>
#include<bitset>
#include<stack>
#include<memory>
#include<numeric>
using namespace std;
using namespace std::chrono;
typedef long long int llint;
typedef long double lldo;
#define mp make_pair
#define mt make_tuple
#define pub push_back
#define puf push_front
#define pob pop_back
#define pof pop_front
#define fir first
#define sec second
#define res resize
#define ins insert
#define era erase
/*cout<<fixed<<setprecision(20);cin.tie(0);ios::sync_with_stdio(false);*/
const int mod=998244353 ;
const llint big=2.19e15+1;
const long double pai=3.141592653589793238462643383279502884197;
const long double eps=1e-10;
template <class T,class U>bool mineq(T& a,U b){if(a>b){a=b;return true;}return false;}
template <class T,class U>bool maxeq(T& a,U b){if(a<b){a=b;return true;}return false;}
llint gcd(llint a,llint b){if(a%b==0){return b;}else return gcd(b,a%b);}
llint lcm(llint a,llint b){if(a==0){return b;}return a/gcd(a,b)*b;}
template<class T> void SO(T& ve){sort(ve.begin(),ve.end());}
template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());}
template<class T>llint LBI(const vector<T>&ar,T in){return lower_bound(ar.begin(),ar.end(),in)-ar.begin();}
template<class T>llint UBI(const vector<T>&ar,T in){return upper_bound(ar.begin(),ar.end(),in)-ar.begin();}
//17:00~

int main(void){
	cout<<fixed<<setprecision(20);cin.tie(0);ios::sync_with_stdio(false);
	int n,a=2;cin>>n;
	while(a*2<=n){a*=2;}
	cout<<a<<endl;
	return 0;
}

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

#pragma GCC optimize "O3"
#define rep(i,a,n) for(long long i=a; i<n; i++)
typedef long long ll;
typedef pair<int,int> P;
const ll MOD = (int)1e9+7;
const ll INF = MOD*MOD;
const double EPS = 1e-9;
const ll powll = 1LL<<1;

/*
while(!frag && cin >> a >>b, a|b)
*/

int main(void){
    int n; cin >> n;
    int p = 2;
    int ans = 0;
    for(int i = 1; i <= 30; i++){
        // cout << p << "\n";
        if(p <= n){
            ans = p;
        }
        p*=2;
    }
    cout << ans <<"\n";
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <stdio.h>
#include <algorithm>
#include <cmath>
#include <stack>
#include <istream>
#include <map>
#include <set>
#include <queue>
#include <functional>
#define rep0(i,n) for (int i = 0; i < (n); ++i)  //0スタート
#define rep1(i,n) for (int i = 1; i < (n); ++i)  //1スタート
#define REP(i,a,b) for (int i = a; i < (b); ++i)  //aからb - 1まで
#define mREP(i,a,b) for (int i = a; i > (b); --i)  //aからb - 1まで
#define p(x) cout<<x<<endl  //xを改行付きで出力
const int INF = 1000000007;  //最大値兼MOD
//  cin.tie(0);
//  ios::sync_with_stdio(false);
typedef long long ll;
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
int main(){
  int n;
  cin >> n;
  int i = 2;
  while(1){
    if(n < pow(2,i)){
      cout<<pow(2,i - 1)<<endl;
      return 0;
    }
    i++;
  }
  return 0;
}

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

int main(){

    int N;
    cin >> N;
    int A=2;
    
    for(int i=1;i<=N;i++){
        if (i==A*2){
           A=A*2;
        }
    }

    cout << A << endl;

    }

C++: #include <cstdio>
int main() {
    int N; scanf("%d", &N);
    int A = 1;
    while(A <= N) A <<= 1;
    printf("%d\n", A >> 1);
}