//#include<iostream>
#include<fstream>
using namespace std;
//unsigned long long int v[14];
int prim(int c)
{
    int nr=0;
    int p=5;
    while(c/p)
        {
        nr=nr+c/p;
        p=p*5;
    }
    return nr;
}
int main ()
{
    int p, a=1, b, c, sol=0;
    ifstream g ("fact.in");
    ofstream h ("fact.out");
    g>>p;
    if(!p) {h<<"1"; return 0;}
    b=p*10;
    while(a<=b && !sol)
    {
    c=(a+b)/2;
    if(prim(c)>p)
        b=c-1;
    else if (prim(c)<p)
        a=c+1;
    else
        sol=c;
    }
    if(sol)
    h<<sol - sol%5;
    else
        h<<"-1";


    g.close();
    h.close();
    return 0;
}