#include<iostream>
#include<string>
using namespace std;
const int maxsize=100;
class seqstack
{
private:
char date[maxsize];
char top;
public:
seqstack()
{
top=-1;
}
~seqstack(){}
char push(char x)
{
if(top==maxsize-1)
{
cout<<"shangyi"<<endl;
}
else
{
date[++top]=x;
return x;
}
}
char pop()
{
if(top==-1)
{
cout<<"xiayi"<<endl;
}
else
{
char x=date[top--];
return x;
}
}
void qkseq()
{
top=-1;
}
};
class dui
{
private:
char front,rear;
char date[maxsize];
public:
dui()
{
front=rear=maxsize-1;
}
~dui(){}
char indui(char x)
{
if((rear+1)%maxsize==front)
{
cout<<"shangyi"<<endl;
}
else
{
rear=(rear+1)%maxsize;
   date[rear]=x;
return x;
}
}
char showdui()
{
char i=(front+1)%maxsize;
return date[i];
}
void qkdui()
{
front=rear=0;
}
};
int main()
{
seqstack seq;
char a;
cin>>a;
seq.push(a);
dui d1,d2;
d1.indui(seq.push(a));
seq.pop();
d2.indui(seq.pop());
if(d1.indui(seq.push(a))==d2.indui(seq.pop()))
cout<<"no"<<endl;
else if(d1.indui(seq.push(a))!=d2.indui(seq.pop()))
cout<<"yes"<<endl;
}