#include <bits/stdc++.h>
using namespace std;
inline int D() {
  int t;
  scanf("%d", &t);
  return t;
}
inline long long LLD() {
  long long t;
  scanf("%lld", &t);
  return t;
}
bool super(long long n) {
  int cnt4 = 0, cnt7 = 0;
  while (n > 0) {
    if (n % 10 == 4)
      cnt4++;
    else
      cnt7++;
    n /= 10;
  }
  return cnt4 == cnt7;
}
int main() {
  vector<long long> v;
  v.push_back(0);
  int i = 0;
  while (v[i] <= 1000000000) {
    long long curr = v[i];
    v.push_back(curr * 10 + 4);
    v.push_back(curr * 10 + 7);
    ++i;
  }
  int x = D();
  for (int z = 0; z < v.size(); z++) {
    if (v[z] >= x && super(v[z])) {
      cout << v[z];
      return 0;
    }
  }
}
