#include <iostream>
#include <fstream>

using namespace std;

unsigned long long f(unsigned long long x)
{
    unsigned long long s=0;
    while(x>0)
    {
        s+=x/5;
        x/=5;
    }
    return s;
}

int main()
{
    ifstream in("fact.in");
    ofstream out ("fact.out");
    unsigned long long p;
    unsigned long long st=1,dr=1e18,m,x;
    in>>p;

    if(p==0)
    {
        out<<1;
        return 0;
    }
    while(st<=dr){
        m=(st+dr)/2;
        x=f(m);
        if(x==p)
        {
            if(f(m-1)!=p)
            {
                out<<m;
                return 0;
            }
            dr=m;
        }
        if(x<p)
            st=m+1;
        else
            dr=m-1;
    }
    out<<-1;
    return 0;
}