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

int main(void)
{
    char S[21];
    int length, i;
    scanf("%s", S);
    length = strlen(S);
    if (length % 2) puts("NO");
    else {
        for (i = 0; i < length / 2; ++i) {
            if (S[i] != S[length / 2 + i]) break;
        }
        if (i == length / 2) puts("YES");
        else puts("NO");
    }
    return 0;
}