#include <stdio.h>
#include <reg51.h>
unsigned long mul(int n);
       int main()
      {
          int m;
		  SCON = 0x50; 
TMOD |= 0x20; 
TH1 = 0xf3; 
TR1 = 1;
TI = 1; 

          puts("Calculate n! n=?\n");
          scanf("%d",&m);
          printf("%d!=%ld\n",m,mul(m));
          getchar();
      }
        unsigned long mul(int n)
     {
          unsigned long p;
          if(n>1)
               p=n*mul(n-1); 
          else
               p=1L;
          return(p);
     }