题解

题解：

#include<iostream>
#include<stack>
using namespace std;
stack<char>a;
int main(){
    int n=0;
    char b;
    while(n<1){
        cin>>b;
        if(b=='('){
            a.push('(');
        }else if(b==')'){
            if(a.empty()!=0){
                cout<<"NO";
                return 0;
            }else{
                a.pop();
            }
        }
        if(b=='@'){
            n++;
        }
    }
    if(a.empty()==0){
        cout<<"NO";
        return 0;
    }
    cout<<"YES";
}