#include<fstream>
#include<bitset>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bitset<2000001> a;
int main()
{
    int k=1,n;
    cin>>n;
    for(int i=3;i*i<=n;i+=2)
        if(!a[i])
            for(int j=i*i;j<=n;a[j]=1,j+=2*i);
    for(int i=3;i<=n;i+=2)
        if(!a[i])
            ++k;
    return cout<<k,0;
}