#include<iostream>
#include<cstdio>
using namespace std;
bool c[200001];

void ciur(int n)
{
    int i,j;
	for(i=2;i*i<=n;i++)
    {
        if(!c[i])  
            for(j=i*i;j<=n;j+=i)
                c[j]=true;
    }
}    

int main()
{
	int n,i,s=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	cin>>n;
	ciur(n);
	for(i=2;i<=n;i++)
	{
		if(c[i]==1)
			s++;
	}
cout<<s-1;
return 0;
}