// Backtracking/recursive generation of "super lucky" numbers (digits 4/7 only,
// equal count of each).
#include <bits/stdc++.h>
using namespace std;

bool isSuperLucky(long long n) {
    int fours = 0, sevens = 0;

    while (n > 0) {
        int digit = n % 10;

        if (digit == 4)
            fours++;
        else if (digit == 7)
            sevens++;

        n /= 10;
    }

    return fours == sevens;
}

long long answer = -1;

void generate(long long x, long long n,int i=11) {

    if (i==0)
        return;

    if (x >= n && isSuperLucky(x)) {
        if (answer == -1 || x < answer)
            answer = x;
    }

    generate(x * 10 + 4, n,i-1);
    generate(x * 10 + 7, n,i-1);
}

int main() {
    long long n;
    cin >> n;

    generate(0, n,11);

    cout << answer << '\n';

    return 0;
}