#include<bits/stdc++.h>
using namespace std;
typedef	long long ll;
vector<ll>	a;
ll N;
void	dfs(ll now, int four, int seven)
{
	if (now > 100000000000ll) return;
	if (four == seven) {a.push_back(now);}
    //cout<<now<<endl;
	dfs(now * 10 + 4, four + 1, seven);
	dfs(now * 10 + 7, four, seven + 1);
}
 
int	main()
{
	cin >> N;
	a.clear();
	dfs(0, 0, 0);
	sort(a.begin(), a.end());
	int u = 0;
	for (; a[u] < N; ++u);
	cout << a[u] << endl;
 
	return 0;
}
 

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