#include <fstream.h>
#include <math.h>

ifstream f("fact.in");
ofstream g("fact.out");

int p,m,i,ok=1,nr;
long n;

int main()
{
    f>>p;
    if(p==0) g<<"1"<<"\n";
    else
    {
        n=p*5;
        for(i=2;i<sqrt(n)&&ok;++i) if(pow(5,i)<=n) m=m+i-1;
                                   else ok=0;
        nr=(p-m)*5;
        g<<nr<<"\n";
    }
    f.close();
    g.close();
    return 0;
}