#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long check(long long);
int main()
{
    long long n, rez = -1, st = 1, dr = 500000000ll;
    f >> n;
    while (st <= dr)
    {
        long long mid = (st + dr) / 2;
        long long ax = check(mid);
        if (ax > n)
            dr = mid - 1;
        else if (ax < n)
            st = mid + 1;
        else
            rez = mid, dr = mid - 1;
    }
    g << rez;
    return 0;
}
long long check(long long nr)
{
    long long n5 = 0;
    for (long long t = 5; t <= nr; t *= 5)
        n5 += nr / t;
    return n5;
}