matching brackets

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n,m=0,k=0,i,j;
    stack<char>a,b,c;
    string s;
    cin>>s;
    if(s[0]==')'||s[0]=='}'||s[0]==']'){cout<<"No"<<endl;return 0;}
    for(i=0;i<s.length();i++)
    {

            if(s[i]=='('||s[i]=='{'||s[i]=='[')
                {a.push(s[i]);
                m++;//cout<<s[i]<<endl;
                }
          else {
                if(a.size()==0 && (s[i]==')'||s[i]=='}'||s[i]==']'))
                {
                    cout<<"No"<<endl;
                    return 0;
                }

           if(s[i]==')'&& a.top()=='(')
            {
                a.pop();


            }
            if(s[i]=='}'&&a.top()=='{')
            {
                a.pop();

            }
             if(s[i]==']'&&a.top()=='[')
            {
               a.pop();
            }

    }
            }
    if(a.empty()==0)
    {
        cout<<"No"<<endl;
    }
    else
    {
        cout<<"Yes"<<endl;

    }


}