#include <bits/stdc++.h>

using namespace std;

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

int p, k=1;
double n;

int main()
{
    fin>>p;

    if(!p)
        fout<<1;
    else if(p<=5)
        fout<<5*p;
    else
    {
        while(k*5<=p)
            k*=5;
        n=(double)(p*4*k)/(k-1);
        n=(int)(n+5)/5*5;
        if(k*5<n)
        {
            k*=5;
            n=(double)(p*4*k)/(k-1);
            if(n!=(int)n)
                n=(int)(n+5)/5*5;
        }
        fout<<n;
    }

    return 0;
}