附上代码：

#include<iostream>
#include<string>
using namespace std;
string a;
long Left=0, Right=0, l1=0, r1=0, g;
long alen;
int main(){
	getline(cin, a);
	alen=a.size();
	for(long i=0;a[i]!='@';i++){
		if(a[i]=='('){
			Left++;
			l1=i;
		}else if(a[i]==')'){
			Right++;
			r1=i;
		}
	}
	if(a.empty()==1)printf("YES"); 
	else if(Left+Right==1)printf("YES");
	else if(Left!=Right||r1<l1)printf("NO");
	else printf("YES");
	return 0;
}