palin.c

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

int main(int argc, char *argv[])
{
	char string[100], reverse_string[100];
	scanf("%s", string);

	for(int i=0, n = strlen(string); i<n; i++)
		if(string[i] == '.') {
			if(string[n-i-1] == '.')
				string[i] = string[n-i-1] = 'a';
			else
				string[i] = string[n-i-1];
		}	

	strcpy(reverse_string, string);
	for(int i=0, n=strlen(string); i<n/2; i++)
		reverse_string[i]^=reverse_string[n-i-1]^=reverse_string[i]^=reverse_string[n-i-1];	

	
	if(strcmp(reverse_string, string)==0)
		printf("%s\n", string);
	else
		printf("-1\n");
	return 0;
}