#include <iostream>
#include <fstream>

using namespace std;


long long int tester(long long int nr);

int P;

int main()
{
    long long int left, right, middle, fact;
    long long int rezult = -1;

    freopen("fact.in", "rt", stdin);
    freopen("fact.out", "wt", stdout);
    cin >> P;

    if(P == 0)
        cout << 1;
    else{
        left = 1;
        right = P * 5;

        while(left <= right){
            middle = (left + right) / 2;
            fact = tester(middle);

            if(fact == P){
                rezult = middle;
                break;
            }
            else if(fact < middle)
                left = middle + 1;
            else
                right = middle - 1;
        }

        if(rezult == -1)
            cout << rezult;
        else
            cout << (rezult - rezult % 5);

    }

    return 0;
}

long long int tester(long long int nr)
{
    int nulla = 0, i = 5;
    while(nr >= i){
        nulla += nr / i;
        i *= 5;
    }
    return nulla;
}