#include <iostream>
#include <fstream>
using namespace std;
ifstream fi("factorial.in");
ofstream fo("factorial.out");

long long solve(int val)
{
    long long put = 5;
    long long amount = 0;
    while(put <= val)
    {
        amount += (val/put);
        put *= 5;
    }
    return amount;
}

int main()
{
    long long zeros;
    fi>>zeros;
    long long n = zeros;
    long long bigAmount = 0;
    if(zeros == 0)
    {
        fo<<1;
        return 1;
    }
    while(solve(n) < zeros)
        n++;

    if(solve(n) != zeros)
        fo<<-1;

    fo<<n;



}