#include <fstream>
using namespace std;
ifstream cin ("fact.in");
ofstream cout ("fact.out");
long long f(long long x)
{
    long long cnt = 0, p = 5;
    while (x >= p)
    {
        cnt += x / p;
        p*=5;
    }
    return cnt;
}
int main()
{
    long long n;
    cin >> n;
    long long st = 1, dr = 500000015;
    while (st<=dr)
    {
        long long mid = (st+dr)/2;
        if (f(mid) < n)
        {
            st = mid+1;
        }
        else
        {
            dr = mid-1;
        }
    }
    cout << (f(st) == n ? st : -1);
}