#include <bits/stdc++.h>
using namespace std;
bool IsPrime(int x){
if(x == 2 || x == 3)
return true;
if(x % 6 != 1 && x % 6 != 5)
return false;
int x_sqrt = (int)sqrt(x);
for(auto i = 5;i <= x_sqrt;i+=6){
if(x % i == 0 || x % (i+2) == 0)
return false;
}
return true;
}
int GetNextFactor(int factor){
if(factor == 2)
return 3;
int f;
for(f = factor + 2;true;f += 2){
if(IsPrime(f))
return f;
}
return -1;
}
/*因式分解*/
void func(int x,map<int,int> &ret){
int factor = 2;
while(x != 1){
if(x % factor == 0){
++ret[factor];
x /= factor;
}
else{
factor = GetNextFactor(factor);
}
}
}
int main(){
int n;
while(cin >> n){
/*因式分解后2的個(gè)數(shù)和5的個(gè)數(shù)*/
int num2 = 0,num5 = 0;
map<int,int> ret;
for(auto i = 2;i <= n;++i){
ret.clear();
func(i,ret);
for(auto it = ret.begin();it != ret.end();++it){
if(it->first == 2)
num2 += ret[it->first];
if(it->first == 5)
num5 += ret[it->first];
}
}
cout<<min(num2,num5)<<endl;
}
return 0;
}
