#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int p;

int Zero(int nr){
    int k = 0, nr2 = nr;
    while(nr >= 5){
        k += nr / 5;
        nr /= 5;
    }
    return k;
}

int Search(){
    int st = -1, dr = p*5, m, k=-1;
    while(dr - st > 1){
        m = dr + (st-dr)/2;
        k = Zero(m);
        if(k >= p) dr = m;
        else st = m;
    }
    if(Zero(m) == p) return m;
        else
            m++;
    if(Zero(m) == p) return m;
    return -1;
}

int main()
{
    fin>>p;
    if(p == 0) fout<<1;
    else fout<<Search();

    return 0;
}