#include <fstream>

using namespace std;

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

int p5[13]={0, 5, 25, 125, 625, 3125, 15625, 78125, 390625, 1953125, 9765625, 48828125, 244140625};

int main()
{
    long long sol, st, dr, mijl, p, i, s, cnr;
    cin>>p;
    st=1;
    dr=400000015;
    sol=-1;
    while(st<=dr)
    {
        mijl=(st+dr)/2;
        i=1;
        s=0;
        while(p5[i]<=mijl&&i<=12)
        {
            cnr=mijl;
            cnr/=p5[i];
            s+=cnr;
            i++;
        }
        if(s==p)
        {
            sol=mijl;
            dr=mijl-1;
        }
        else if(s>p)
        {
            dr=mijl-1;
        }
        else
        {
            st=mijl+1;
        }
    }
    cout<<sol;
    return 0;
}