#include "stdio.h"
#include "malloc.h"
#include "string.h"
 
int main()
{
    FILE *f,*g;
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    int x,s,p;
	fscanf(f,"%d",&x);
    if(x==0)
        fprintf(g,"%d",1);
    else
    {
		p = 5;
		s = 0;
        while(p<=x)
		{
			s += x/p;
			p*=5;
		}
		fprintf(g,"%d",s);
    }
    return(0);
     
}