#include <fstream>
using namespace std;
ifstream fin ("fact.in");
ofstream fout ("fact.out");
long long p,st,dr,mij,x,p5,s;
int main()
{
    fin>>p;
    st=1;
    dr=p*5;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        x=mij;
        p5=5;
        s=0;
        while (p5<=x)
        {
            s=s+x/p5;
            p5=p5*5;
        }
        if (s<p)
            st=mij+1;
        else
            dr=mij-1;
    }
    p5=5;
    s=0;
    x=st;
    while (p5<=x)
    {
        s=s+x/p5;
        p5=p5*5;
    }
    if (s==p)
        fout<<st;
    else
        fout<<-1;
    return 0;
}