#include <iostream>
using namespace std;
int main (){
char *cadena = ( char* ) calloc ( 30, sizeof ( char ) );
printf ( "%s", "Introduce una cadena MAX. 30 : " );
scanf ( "%s", cadena );
getchar ();
int tam = strlen ( cadena );
int a;
if ( tam % 3 == 0 )
a = tam + tam / 3 - 1;
else
a = tam + tam / 3;
realloc ( cadena, a * sizeof ( char ) );
char *cadena1 = ( char* ) calloc ( a, sizeof ( char ) );
for ( int i = tam, j = 0, k = a; i >= 0; i--, j++, k-- ){
if ( j % 3 == 0 && j != 0 ){
cadena1[k] = cadena[i];
k--;
cadena1[k] = '.';
}
else{
cadena1[k] = cadena[i];
}
}
memcpy ( cadena, cadena1, a );
free ( cadena1 );
printf ( "%s", cadena );
getchar();
return 0;
}