#include <bits/stdc++.h>
using namespace std;
const int N = 100100;
char x[N];
int main() {
  scanf("%s", x + 1);
  x[0] = '0';
  int k = strlen(x + 1);
  if (k % 2 == 1) {
    k = k / 2 + 1;
    for (int i = 0; i < k; i++) printf("4");
    for (int i = 0; i < k; i++) printf("7");
    puts("");
    return 0;
  }
  for (int i = k; i >= 1; i--) {
    if (x[i] >= '8') {
      x[i] = '0';
      x[i - 1] += 1;
    }
  }
  if (x[0] == '1') {
    k += 1;
    if (k % 2 == 1)
      k = k / 2 + 1;
    else
      k = k / 2;
    for (int i = 0; i < k; i++) printf("4");
    for (int i = 0; i < k; i++) printf("7");
    puts("");
    return 0;
  }
  int h = k / 2;
  int h4 = h, h7 = h;
  bool ok = false;
  for (int i = 1; i <= k; i++) {
    if (!ok) {
      if (x[i] < '4' && h4 > 0) {
        x[i] = '4';
        ok = true;
        h4--;
      } else if ((x[i] > '4' && x[i] < '7') || x[i] < '4') {
        x[i] = '7';
        ok = true;
        h7--;
      } else if (x[i] == '4' && h4 > 0)
        h4--;
      else {
        x[i] = '7';
        h7--;
      }
    } else {
      if (h4 > 0) {
        h4--;
        x[i] = '4';
      } else {
        x[i] = '7';
        h7--;
      }
    }
  }
  if (h4 == 0 && h7 == 0) {
    for (int i = 1; i <= k; i++) printf("%c", x[i]);
    puts("");
  } else {
    int now = 0, idx;
    for (int i = 1; i <= k; i++) {
      if (x[i] == '7') now += 1;
      if (now == h) {
        idx = i;
        break;
      }
    }
    bool has4 = false;
    for (int i = idx; i >= 1; i--) {
      if (x[i] == '4') {
        has4 = true;
        idx = i;
        break;
      }
    }
    if (has4) {
      x[idx] = '7';
      h4 = h7 = h;
      for (int i = 1; i <= idx; i++) {
        if (x[i] == '4') h4--;
        if (x[i] == '7') h7--;
      }
      for (int i = idx + 1; i <= k; i++) {
        if (h4 > 0) {
          h4--;
          x[i] = '4';
        } else
          x[i] = '7';
      }
      for (int i = 1; i <= k; i++) printf("%c", x[i]);
      puts("");
    } else {
      k += 2;
      k = k / 2;
      for (int i = 0; i < k; i++) printf("4");
      for (int i = 0; i < k; i++) printf("7");
      puts("");
    }
  }
}
