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

int main(void)
{
	char s[21];
	int judge = 0;
	int i;

	scanf("%s", s);

	if (!(strlen(s) % 2)) {
		for (i = 0; i < strlen(s) / 2; i++) {
			if (s[i] != s[i + strlen(s) / 2]) 
				goto print;
		}
		judge++;
	}
print:
	printf("%s\n", judge ? "YES" : "NO");

	return 0;
}