#include <fstream>

using namespace std;

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

long long st,dr,p;

int main()
{
    in>>p;
    st=1;
    dr=5e8;
    while ( st<=dr)
    {
        long long aux=(st+dr)/2;
        long long rez=0;
        while ( aux>0)
        {
            rez+=(aux/5);
            aux/=5;
        }
        if ( rez>=p)
            dr=(st+dr)/2-1;
        else
            st=(st+dr)/2+1;
    }
    long long aux=st;
    long long rez=0;
    while ( aux>0)
    {
        rez+=(aux/5);
        aux/=5;
    }
    if ( rez==p)
        out<<st;
    else
        out<<-1;
    return 0;
}