#include <fstream>

using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
long long p;
bool putere (int a,int b)
{
    long long s=0;
    while(a)
    {
        a=a/5;
        s+=a;
    }
    if(s<b)
        return true;
    return false;
}
bool puter (int a,int b)
{
    long long s=0;
    while(a)
    {
        a=a/5;
        s+=a;
    }
    if(s==b)
        return true;
    return false;
}
int main()
{
    long long k=0,pas=1<<30;
    in>>p;
    while(pas)
    {
        if(putere(k+pas,p))
            k+=pas;
        pas/=2;
    }
    if(puter(k+1,p))
        out<<k+1;
    else
        out<<-1;
    return 0;
}