#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
#define ll long long
ll p;
ll calc_nr0(ll x)
{
    ll put=5,rez=0;
    while(x/put>0)
    {
        rez=rez+x/put;
        put*=5;
    }
    return rez;
}
int main()
{
    fin>>p;
    ll st,dr,mij;
    st=1;
    dr=1e18;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(calc_nr0(mij)==p && (mij==1 || calc_nr0(mij-1)<p))
        {
            fout<<mij;
            return 0;
        }
        else if(calc_nr0(mij)==p || calc_nr0(mij)>p)
            dr=mij-1;
        else
            st=mij+1;

    }
    fout<<-1;
}