#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
bool check(int, int);
int main()
{
    int n, rez;
    f >> n;
    int st = 0, dr = INT_MAX;
    while (st <= dr)
    {
        int mid = st + (dr - st) / 2;
        if (check(mid, n))
            rez = mid, dr = mid - 1;
        else
            st = mid + 1;
    }
    g << rez;
    return 0;
}
bool check(int nr, int mn)
{
    int n2 = 0;
    for (int t = 2; nr / t > 0; t *= 2)
        n2 += nr / t;
    int n5 = 0;
    for (int t = 5; nr / t > 0; t *= 5)
        n5 += nr / t;
    return min(n2, n5) >= mn;
}