#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define pb push_back

ll n;
vector <ll> a;

void rec(int q, int w, ll e)
{
    if (q == w && e >= n)
    {
        a.pb(e);
    }
    if (q + w > 10)
    {
        return;
    }
    rec(q+1,w,(ll)(e*10+4));
    rec(q,w+1,(ll)(e*10+7));
}

int main ()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    rec(0,0,0);
    sort(a.begin(),a.end());
    cout << a[0];
    return 0;
}