#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
typedef struct node{
    int data;
    struct node*next;
}Node;
Node*head =NULL,*tail=NULL;
void create (int num){
    Node *newNode=(Node*)malloc(sizeof(Node));
    newNode->data=num;
    newNode->next =NULL;
    if(!head)head=tail=newNode;
    else{
        tail->next=newNode;
        tail=newNode;
    }
}
    int ispalindrome(){
        int a[100],i=0,j;
        Node*t=head;
        while(t){a[i++]=t->data;t=t->next;
        for(j=0;j<1/2;j++)
         if(a[j]!=a[i-j-1])
         return 0;
         return 1;
    }
    int main()
    {
        char s[50];int n;
        while(scanf("%s",s)==1){
            int k=0;
            if(s[0]!='-'&&!isdigit(s[0])){printf("Invalid input");
            return 0;
        }
        for(k=1;s[k];k++)if(!isdigit(s[k]))
        {
            printf("Invalid input");
            return 0;
        }
        n=atoi(s);
        if(n==-1)
        break;
        create( n);
      }
       printf(ispalindrome()?"yes":"no");
    }