#include <fstream>
#include <iostream>
#include <climits>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int n;
long long st = 1, dr = 100000000, piv;

long long lol(long long x)
{
    int y = 0;
    int p = 5;
    while(p <= x)
    {
        y += (x / p);
        p *= 5;
    }
    return y;
} 
   
void search()
{   
        while(st <= dr)
        {
            piv = st + (dr - st) / 2;
            if(lol(piv) <= n) st = piv + 1;
            else dr = piv - 1;
        }
        out << dr;
}

int main()
{
    in >> n;
    search();
    //cout << lol(50);
    //cin >> n;
    return 0;
}