#include<stdio.h>
#include <string.h>

int main(void){
    char s[21];
    int len,i,h;
    
    scanf("%s",s);
    h = strlen(s)/2;
    if(strlen(s)%2 == 0){
        for(i=0;i<h;i++){
            if(s[i] != s[h+i]){
                printf("NO\n");
                return 0;
            }
        }
    }
    else{
        printf("NO\n");
        return 0;
    }
    
    printf("YES\n");
    return 0;
}