#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
int cate0(int mijl)
{
    int nr0;
    long long p5;
    nr0=0;
    p5=5;
    while (p5<=mijl)
    {
        nr0=nr0+mijl/p5;
        p5=p5*5;
    }
    return nr0;
}
int main()
{
    long long p,st,dr,mijl;
    f>>p;
    st=1;
    dr=5*p;
    while (st<=dr)
    {
        mijl=(st+dr)/2;
        if (cate0(mijl)<p)
            st=mijl+1;
        else
            dr=mijl-1;
    }
    if (cate0(st)==p)
        g<<st;
    else
        g<<"-1";
    return 0;
}