#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#include <fstream>
#include <vector>

using namespace std;

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

vector<int> mp(1000001);

int main()
{
    for (int i = 5; i <= 1000000; i += 5)
    {
        int c = i;
        while (c % 5 == 0)
        {
            mp[i] ++;
            c /= 5;
        }
    }
    for (int i = 1; i <= 1000000; i ++)
    {
        mp[i] += mp[i - 1];
    }
    int p; cin >> p;
    cout << lower_bound(mp.begin() + 1, mp.end(), p) - mp.begin() << '\n';
}