Petya loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn‘t contain digits other than 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Lucky number is super lucky if it‘s decimal representation contains equal amount of digits 4 and 7. For example, numbers 47, 7744, 474477 are super lucky and 4, 744, 467 are not.

One day Petya came across a positive integer n. Help him to find the least super lucky number which is not less than n.

Input

The only line contains a positive integer n (1?≤?n?≤?10⁹). This number doesn‘t have leading zeroes.

Output

Output the least super lucky number that is more than or equal to n

Please, do not use the %lld specificator to read or write 64-bit integers in C++. It is preferred to use the cin, cout streams or the %I64d specificator.

Example

4500

4747

47

47

 1 #include<cstdio>
 2 #include<string>
 3 #include<cstring>
 4 #include<iostream>
 5
 
 #include<algorithm>
 6 using namespace std;
 7 typedef long long ll;
 8 
 9 const long long int INF=10000000000000;
10 
11 ll n,ans,mcnt;
12 char vis[12][2];
13 int a[12][2]={{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7},{4,7}};
14 
15                
16 void DFS(ll p,ll q,int cnt,int x,int y)
17 {   ll tem=p*10+q;
18     if(tem>=n&&x==y) ans=min(ans,tem);
19     if(cnt==mcnt||cnt>12) return;
20     
21     for(int i=0;i<2;i++){
22         if(vis[cnt][i]) continue;
23         vis[cnt][i]=true;
24         
25         if(a[cnt][i]==4) DFS(tem,a[cnt][i],cnt+1,x+1,y);
26         if(a[cnt][i]==7) DFS(tem,a[cnt][i],cnt+1,x,y+1);
27          vis[cnt][i]=false;
28     }
29 }
30 
31 int main()
32 {    while(cin>>n){
33         memset(vis,false,sizeof(vis));
34         mcnt=0,ans=INF;
35         int nn=n;
36         while(nn){
37             nn=nn/10;
38             mcnt++;
39         }
40         if(mcnt%2==0) mcnt+=2;
41         if(mcnt%2!=0) mcnt+=1;
42         DFS(0,0,0,0,0);
43         cout<<ans<<endl;
44     }     
45     return 0;
46 }

Lucky Numbers (easy) CodeForces - 96B