#include<bits/stdc++.h> using namespace std;

const int N=1e5+5;

int main(){ int A; int count =0; cin >> A; if(A % 10 == 5){ while(1){ if(A % 5 == 0 ){ count++; A /= 5; } else { break; } } cout << count << endl; } else{ while(A){ if(A % 10 == 0){ count ++; } A /= 10 ; } cout << count << endl; } return 0; }