CodeForces Beta Round # 77 (div2, task B)

#include <cstdio>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long LL;

LL res = LL(1e16), n;

void rec(LL now, int f, int s)
{
    if (now > res)
        return;
    if (now >= n)
    {
        if (f == s)
        {
            res = min(now, res);
            return;
        }
    }
    rec(now * 10 + 4, f + 1, s);
    rec(now * 10 + 7, f    , s + 1);
}

int main()
{
    cin >> n;
    rec(0, 0, 0);
    cout << res;
    return 0;
}