include <bits/stdc++.h>

using namespace std;

int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n; cin >> n;
int cnt = 0;
if(n == 0) return 1;
else if(n < 5) return 0;
else{
for(int i = 5; i <= n; i+=5){
int tmp = i;
while(tmp % 5 == 0){
cnt++;
tmp /= 5;
}
}
cout << cnt;
}
}