#include <bits/stdc++.h>

using namespace std;

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

int nr_zero(int n){
    int nr;

    while(n >= 5){
        nr += n / 5;
        n /= 5;
    }
    return nr;
}

int caut_bin(int n, int p){
    int st, dr, mij, rez;
    st = 1;
    dr = 5 * 100000000;

    while(st <= dr){
        mij = (st + dr) / 2;

        if(nr_zero(mij) >= p){
            rez = mij;
            dr = mij - 1;
        }else{
            st = mij + 1;
        }
    }
    if(nr_zero(rez) != p){
        rez = -1;
    }
    return rez;
}
int main()
{
    int n, p;

    fin >> p;
    fout << caut_bin(n, p);
    return 0;
}