#include<iostream.h>
#include<stdlib.h>
#include<string.h>

const int MaxListsize=100;
const int MaxQueuesize=100;

typedef char DataType;

class SeqQueue
{
private:
	DataType data[MaxQueuesize];
	int front;
	int rear;
	int count;
public:
	SeqQueue(void){front=rear=0;count=0;}
	~SeqQueue(void){}
	void Qinsert(const DataType& item);
	DataType QDelete(void);
	DataType QFront(void)const;
	int QueueEmpty(void)const{return front==rear;}
	void ClearQueue(void){front=rear=0;count=0;}
	int GetSize(void)const{return count;}
};
void SeqQueue::Qinsert(const DataType& item)
{
	if(count==MaxQueuesize)
	{
		cout<<"隊(duì)列已滿"<<endl;
		exit(0);
	}
	data[rear]=item;
	rear=(rear+1)%MaxQueuesize;
	count++;
}
DataType SeqQueue::QDelete(void)
{
	DataType temp;
	if(count==0)
	{
		cout<<"隊(duì)列已空"<<endl;
			exit(0);
	}
	temp=data[front];
	front=(front+1)%MaxQueuesize;
	count--;
	return temp;
}
DataType SeqQueue::QFront(void)const
{
	if(count==0)
	{
		cout<<"隊(duì)列空"<<endl;
			exit(0);
	}
	return data[front];
}


 class SeqStack
{
private:
	DataType data[MaxListsize];
	int top;
public:
	SeqStack(void){top=0;}    //構(gòu)造函數(shù)
	~SeqStack(void){}   //析構(gòu)函數(shù)

	void Push(const DataType& item);   //壓棧，壓入item	
	DataType Pop(void);  //退棧
	DataType Peek(void)const;  //讀出棧頂?shù)脑?	int StackEmpty(void)const  //判空
	{
		return(top==0);
	}
	int GetSize(void)const{return top;}	//輸出元素的個(gè)數(shù)	
	void ClearStack(void){top=0;}  //清空棧

};
//---------------------------------
void SeqStack::Push(const DataType& item)
{	
	if(top==MaxListsize){
		cout<<"堆棧已滿！"<<endl;
		exit(0);
	}
  data[top]=item;
  top++;
}

//--------------------------------------------
DataType SeqStack::Pop(void){
	if(top==0){
		cout<<"堆棧已空！"<<endl;
		exit(0);
	}
	top--;
	return data[top];
}
//--------------------------------------------
DataType SeqStack::Peek(void)const{
	if(top==0){
		cout<<"堆棧空！"<<endl;
		exit(0);
	}

	return data[top-1];
}



void main(void){
	SeqStack mystack;
	SeqQueue myqueue;
	char str[80];
	cin.getline(str,80);
	int h=strlen(str);
	for(int i=0;i<h;i++)
	{
		myqueue.Qinsert(str[i]);
		mystack.Push(str[i]);
	}
	while(!myqueue.QueueEmpty())
	{
		if(myqueue.QDelete()!=mystack.Pop())
		{
			cout<<"no"<<endl;
			return;
		}
	}
	cout<<"yes"<<endl;
}