/*
programme for computing number of zeroes at the end of factorial of a given number n
*/
#include<stdio.h>
#include<math.h>        //including math.h header file to use pow function
int main()
{
    int i,n,test=0,count=0;
    //taking input number n
    scanf("%d",&n);
    
    //looping from 1 till loop break
    for(i=1;;i++)
    {
        test=n/pow(5,i);//division of n by ith power of 5(storing in integer form)
        if(test!=0)     //condition for zeroes at end corresponding individual ith case
        {
            count=count+test;  
        }
        else 
            break;      //break the loop for if test=0
    }
    printf("%d\n",count);         
    return 0;
}