#include <bits/stdc++.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
#define int long long

int nr_zerouri(int n)
{
    int p = 5, s = 0;
    while(p <= n)
    {
        s += n / p;
        p *= 5;
    }
    return s;
}

int caut_bin(int p)
{
    int st = 1, dr = 5e8, ans = -1;
    while(st <= dr)
    {
        int mid = (st + dr) / 2;
        if(nr_zerouri(mid) == p)
        {
            ans = mid;
            dr = mid - 1;
        }
        else if(nr_zerouri(mid) > p)
            dr = mid - 1;
        else
            st = mid + 1;
    }
    return ans;
}

signed main()
{
    int p;
    fin >> p;
    fout << caut_bin(p);

    return 0;
}