栈

#include <iostream>
#include <cstring>

using namespace std;

int n, top, mid, next;
char a[100010], s[100010];

int main(){
    cin >> a;
    n = strlen(a);
    mid = n / 2 - 1;
    for(int i = 0; i <= mid; i ++) s[ ++ top] = a[i];
    if(n % 2) next = mid + 2;
    else next = mid + 1;
    for(int i = next; i <= n - 1; i ++){
        if(a[i] != s[top]) break;
        top --;
    } 
    if(top == 0) cout << "yes";
    else cout << "no";
    return 0;
}