lucky sum of digit

A. Lucky Sum of Digits

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Petya wonders eagerly what minimum lucky number has the sum of digits equal to n. Help him cope with the task.

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Input

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The single line contains an integer n (1 ≤ n ≤ 10⁶) — the sum of digits of the required lucky number.

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Output

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Print on the single line the result — the minimum lucky number, whose sum of digits equals n. If such number does not exist, print -1.

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Sample test(s)

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input

11

output

47

input

10

output

-1

一开始没想清楚，乱打bfs和dfs，后面想了下 发现DFS和BFS明显不行。。随便一下就会爆掉。

其实构成n的数只有4，7那么直接把最大的4，和7的个数求出来。然后在这里面暴力就可以解决了。然而最小的数肯定是把4放在最前面。

下面是AC代码：

#include<iostream>
#include<string>
#include<queue>
using namespace std;
int n,i,j,k,flag,sum;
int main()
{
	int s4,s7;
	cin>>n;
	s4=n/4; s7=n/7;
	for(i=0;i<=s4;i++)
	{
		for(j=0;j<=s7;j++)
		{
			if(i*4+j*7==n)
			{
				flag=1;
				break;
			}
		}
		if(flag)  break;
	}
	if(!flag)
		cout<<-1<<endl;
	else
	{
		for(k=1;k<=i;k++)
			printf("4");
		for(k=1;k<=j;k++)
			printf("7");
		printf("\n");
	}

	return 0;
}