YODA

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

char line[1024];
int count[32];
long long unsigned result,n;
int odd;

int main( int argc, char* argv[] ){
loop:
    if( !gets( line ) ) return 0;
    char *ptr = line;
    memset( count, 0, sizeof(count) );
    while( *ptr ){
      if( (*ptr>='A') && (*ptr<='Z') ) { count[ *ptr - 'A' ]++; }
      else if( (*ptr>='a') && (*ptr<='z') ) { count[ *ptr - 'a' ]++; }
      ptr++;
    }
    odd = 0;
    for( int i = 0; i < 26; i++ ){
      if( count[i] & 1 ){
        if( odd ){ printf("0\n"); goto loop; }
        else odd = 1;
      }
      count[i] /= 2;
    }
    result = 1; n = 1;
    for( int i = 0; i < 26; i++ ){
      for( int j = 1; j <= count[i]; j++ ){
        result *= (n++);
        result /= j;
      }
    }
    printf("%llu\n",result);
goto loop;
}