第k个幸运数

//大神看看，这样可以不
#include <string>
using namespace std;

int main()
{
	int num = 16;
	while (cin>>num)
	{
		num--;
		string str;
		int n = log(num / 2 + 1)/log(2);
		int m=num-(1<<(n+1))+2;
		for (int i = 0; i <= n; i++)
		{
			str += (m & 1) ? "7" : "4";
			m >>= 1;
		}
		reverse(str.begin(), str.end());
		cout << str << endl;
	}
	return 0;
}