#include <iostream>
#include <fstream>

using namespace std;

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

long long p, k=1, n=5;

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

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

    return 0;
}