#include <iostream>
#include<fstream>
#include<cstring>
#include<algorithm>
#include<iomanip>
#define N 100005
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

//cautare binara
int p;
int exp5(int x)
{
    int r=5,ct=0;
    while(r<=x)
    {
        ct+=x/r;
        r*=5;
    }
    return ct;

}

void solve()
{
    int s=1,d=p*10,x,m;
    bool gasit=false;
    //cout<<s<<" "<<d;
    while(s<d&&gasit==false)
    {
        m=(s+d)/2;
        //cout<<1;
        x=exp5(m);
       // cout<<x<<" ";
        if(x==p)
         {gasit=true;}
        else
            if(x>p)d=m-1;
            else s=m+1;

    }
    while(m%5!=0)m--;
    //cout<<exp5(m);
    fout<<m;
}

int main()
{

    fin>>p;
    //cout<<exp5(45);
    if(p==0)fout<<1;
    else  solve();


    return 0;
}