checking braces using stack

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string a;
    cin>>a;
    stack <char> s;
    for(int i=0; i<a.size(); i++)
    {
        if(a[i]=='('||a[i]=='{'||a[i]=='[')
        {
            s.push(a[i]);
        }
       else if(a[i]==')'||a[i]=='}'||a[i]==']')
       {
           if(s.empty()||(a[i]==')'&&s.top()!='(')||(a[i]=='}'&&s.top()!='{')||(a[i]==']'&&s.top()!='['))
            {
                cout<<"NO";
                return 0;
            }
            else
                s.pop();
       }
    }
    if(s.empty())
        cout<<"YES";
    else cout<<"NO";
}