#include <fstream>

using namespace std;

fstream f,g;

int p,n,l1,l2,i,nr;

{
    f.open("fact.in",ios_base::in);
    g.open("fact.out",ios_base::out);
    f>>p;
    l1=1;
    l2=5*p;
    while(l1!=l2)
    {
        n=(l1+l2)/2;
        for(i=5,nr=0;i<n;i*=5)nr+=n/i;
        if(nr<=p)l2=n;
        else l1=n+1;
    }
    g<<l1;
}