#include<fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
char a[2000001];
int n,cnt;
int main()
{
	cin>>n;
	a[0]=a[1]=1;
	for(int i=2;i*i<=n;++i)
        if(!a[i])
            for(int j=i;j*i<=n;++j)
                a[i*j]=1;
    for(int i=1;i<=n;++i)
        if(!a[i]) ++cnt;
    cout<<cnt;
}