#include<cstdio>
#include<stdlib.h>
#include<algorithm>
#include<fstream>
#include<iostream>
using namespace std;
int main()
{

    FILE* si=fopen("fact.in","r");
    ofstream so;
    so.open("fact.out");
    int p;
    fscanf(si,"%i",&p);
    int s=0,put=1;
    while(s<p)
    {
        s=s+put;
        put=put*5;
    }
    put=put/5;
    s=s-put;
    int cont=0,x;
    p=p-s;
    while(1)
    {
        s=cont;
        x=cont;
        while(x/5>0)
        {
            x=x/5;
            s=s+x;
        }
        if(s>=p)
            break;
        ++cont;
    }
    put=put+cont*5;
    if(put==0)
        ++put;
    so<<put;
}