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

int fac_lastnum( int n )
{
   int NUM;
   int count = 1;
   NUM=n;
   while(NUM>1)
    { 
            n=NUM;
        	while(n % 10 == 0)         /*消除尾部0*/
         	{
          	    n /= 10;
               	} //while
	n %= 10;
	count *= n;
	while(count % 10 == 0)             /*消除結果尾部的0*/ 
	            {
	            count/=10;
	            }
	count %= 10 ;
	NUM --;
    }
    return count;
}
main(){
	FILE *fp;
    int N , last_0number;
    
	if((fp=fopen("in.date" , "r")) == NULL)
	printf("不能打開in.date");     /*打開in.date文件*/ 
	fscanf(fp , "%d" , &N );       /*讀取N的值*/
    fclose( fp );
    
    last_0number = fac_lastnum(N);          /*計算N！的最后一位非零數(shù)*/ 
    
    if((fp = fopen("out.date" , "w")) == NULL)
    printf("不能打開out.date");              /*打開文件out.date*/
    fprintf( fp , "%d！的最后一位非零數(shù)是：%d", N ,last_0number );
	
    return 1;
       }