// #include <ext/pb_ds/assoc_container.hpp> 
                                             //#include <ext/pb_ds/tree_policy.hpp> 
                                                #include <iostream>
                                                #include <iomanip>
                                                #include <sstream>
                                                #include <cstring>
                                                #include <vector>
                                                #include <deque>
                                                #include <queue>
                                                #include <set>
                                                #include <map>
                                                #include <valarray>
                                                #include <iterator>
                                                #include <functional>
                                                #include <limits>
                                                #include <algorithm>
                                                #include <numeric>
                                                #include <cmath>
                                                #include <cassert>
                                                #include <unordered_map>
                                                #include <unordered_set>
                                                #include <stack>
                                                using namespace std;
                                                #define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
                                                 #define trace(x) cerr << #x << ": " << x << " " << endl;
                                             
                                                typedef int64_t ll;
                                             
                                                #define endl '\n'
                                                #define int ll
                                                ll mod=1e9+7;
                                                ll mod1=1e9+6;
                                                
                                                ll power(ll a,ll b)
                                                {
                                                    if(b==0) return 1;
                                                    else if(b%2==0)
                                                        return power((((a%mod)*(a%mod))%mod),b/2)%mod;
                                                    else return ((a%mod)*(power((((a%mod)*(a%mod))%mod),b/2)%mod))%mod;
                                                }
                                               
                                             //  using namespace __gnu_pbds;
                                           //  #define ordered_set tree<pair<int,int>, null_type,less<pair<int,int>>, rb_tree_tag,tree_order_statistics_node_update>
                                                //find_by_order(k)  returns iterator to kth element starting from 0;
                                                //order_of_key(k) returns count of elements strictly smaller than k;
                                                //erase,insert same as normal set
                                              
                                           
                                            int32_t main()
                                            {
                                                IOS
                                           
                                                    int n;
                                                    cin>>n;
                                                    if(n%2!=0)
                                                    {
                                                        cout<<0<<endl;return 0;
                                                    }
                                                    
                                                    int te=5;
                                                    int ans=0;
                                                    while(1)
                                                    {
                                                        if(n/(2*te)==0)
                                                        {
                                                            break;
                                                        }
                                                        else
                                                        {
                                                            ans+=(n/(2*te));
                                                            te=te*5;
                                                        }
                                                    }
                                                    cout<<ans<<endl;



                                             }    


Measured memory_bytes: 256