#include <iostream>
using namespace std;
int N,A,B;
int main()
{
cin>>N;
for(int x=1; x<=N; x++)
{
int K=x;
while(1)
{
if(K==0) break;
if(K%2==0||K%5==0)
{
if(K%2==0)
{
K/=2;
A++;
}
else if(K%5==0)
{
K/=5;
B++;
}
}
else break;
}
}
if(A>B) cout<<B;
else cout<<A;
}