#include <iostream>
#include <fstream>
#define nmax 10000000
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long p;
long nr;
long rez;
long v[nmax+1];

void fact()
{
    int j;
    for(int i=5;i<=nmax;i+=5)
    {
        j=i;
        while(j%5==0)j/=5,v[i]++;
        v[i]+=v[i-1];
        v[i+1]=v[i+2]=v[i+3]=v[i+4]=v[i];
    }
    //for(int i=1;i<=100;i++)cout<<v[i]<<" ";cout<<endl;
}

int main()
{

    f>>p;
    fact();
    if(p==0)
    {
        g<<1;
        return 0;
    }
    long st=0, dr=nmax, c;
    while(st<=dr)
    {
        //cout<<st<<" "<<dr<<" - ";
        c=(st+dr)/2;

        nr=v[c];

        if(nr==p)
        {
            rez=c;
            dr=c-1;
        }
        else if(nr>p)dr=c-1;
        else st=c+1;
        //cout<<nr<<endl;
    }
    if(rez==0)g<<rez-1;
    else g<<rez;
    return 0;
}