#include <stdio.h>
#include <stdlib.h>


int main()
{
	FILE *input, *output;
	char word[50], *rword, save;
	int s = 0,size = 0, e=1;

			input = fopen("input.txt", "r");


		if (input == NULL)
		{
			printf("File 'input.txt' does not exist");
			fclose(input);
		}
		else
		{
			while((fscanf(input, "%c", &word)!=EOF))
			{
				if(!input) break;
				size+=1;
			}

		}
	if (size>=50)
	{
		printf("Invalid input\n");
		return 0;
	}

		if (size%2==1)
		{
			printf("Invalid input\n");
			return 0;
		}

		else
		for (int i=0; i<size-2/2; i++)
			if(word[i]!=word[size-i-1])
				e=e-1;

	printf("e = %d\n",e);
	int j=size;
	if (e==0)
	{
		for (int i=0;i<size/2;i++)
		{
			word[j+1]=*rword+i;
			j=j-1;
		}
	}
	else
		{
			printf("Invalid input\n");
			return 0;
		}


			for (int i=0;i<size;i++)
			printf("%c",word[i]);


	output = fopen("output.txt", "w");
	  	if (output == NULL)
		{
			printf("File 'output.txt' does not exist");
			fclose(output);
		}
		else
		{
		for (int i=0;i<size;i++)
			fprintf(output,"%c",word[i]);
		}
	fclose(output);
	fclose(input);


	return 0;
}