#include <iostream>
#include <fstream>

using namespace std;

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

long long p, k=1, n;

int main()
{
    fin>>p;
    if(p==0)
        fout<<1;
    else if(p<5)
        fout<<5*p;
    else
    {
        while(k*5<=p)
            k*=5;
        n=(4*p*k)/(k-1);
        if(n%5!=0)
            n=(n+5)/5*5;
        if(k*5>n)
            fout<<n;
        else
        {
            k*=5;
            n=(4*p*k)/(k-1);
            if(n%5!=0)
                n=(n+5)/5*5;
            fout<<n;
        }
    }

    fin.close();
    fout.close();

    return 0;
}