P1928 外星密码

#include<bits/stdc++.h>
using namespace std;
string Read ()
{
	int num;
	string s="",s1="";
	char c;
	while (cin>>c)
	{
		if (c=='\n'||c==' ')
			return s;
		if (c=='[')
		{
			cin>>num;
			s1=Read ();
			while (num--)
				s+=s1;
		}
		else
		{
			if (c==']')
				return s;
			else
				s+=c;
		}
	}
	return s;
}
int main ()
{
	cout<<Read ()<<endl;
	return 0;
}

把第8行的cin>>c改成c=getchar()第九组会MLE，求问原因。