#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int main()
{
    long long nrzero,cinci=0,doi=0,numar=5,valrez=0;
    fin>>nrzero;
    while(nrzero!=0)
    {
        numar=numar+5;
        valrez=numar;
        while(valrez%5==0)
        {
            valrez=valrez/5;
            cinci++;
        }
        //cout<<numar<<" "<<cinci<<" "<<doi;
        //cout<<endl;
        while(cinci!=0)
        {
            cinci--;
            if(nrzero!=0)
                nrzero--;
            else
                cinci=0;

        }
    }
    if(numar!=0)
        fout<<numar-5;
    else
        fout<<1;
    fin.close();
    fout.close();
    return 0;
}