#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
const long long maxn=100000000000000000;
long long n, a, b, res;
long long zero(long long x)
{
    long long res = 0, div = 5;
    while(x / div)
    {
        res += x / div;
        div *= 5;
    }
    return res;
}

int main()
{
    f>>n;
    a = 1;
    bool found = false;
    b = maxn;
    while(a < b)
    {
        long long mid = (a + b) / 2;
        res = zero(mid);
        if(res > n) b = mid - 1;
        else if(res < n) a = mid + 1;
        else b = mid, found = true;
    }
    if(!found) g<<-1<<'\n';
    else g<<a<<'\n';
    f.close();
    g.close();
    return 0;
}