#include <fstream>

using namespace std;

int main()
{
    ifstream f("date.in");
    ofstream g("date.out");
    int n=0,j,i,k,s,p,q=0,cp;
    f>>p;
    cp=p;
    while(cp)
    {
        cp=cp/5;
        q++;
    }
    /*k=5*p;
        s=5;
        i=0;
        while(s<k)
        {
            s=s*5;
            i++;
        }
        j=0;
        s=25;
        while(j<i)
        {
            n+=k/s;
            s*=5;
            j++;
        }*
    cp=p;
    s=5;
    while(s<=cp)
    {
        p=p-p/s;
        s*=5;
    }
    g<<p*5;*/
    k=1;
    while(5*k+(k-1)*k/2<p)
    {
        k++;
    }
    k=k-1;
    g<<(p-k)*5;
    f.close();
    g.close();
    return 0;
}