#include <fstream>
#include <bitset>

using namespace std;
bitset <2000001> a;
int main()
{
    int n,k,i,j;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    k=1;
    for(i=4;i<=n;i+=2) a[i]=1;
    for(i=3;i*i<=n;i+=2){
        if(a[i]==0){
            for(j=i*i;j<=n;j+=2*i) a[j]=1;
        }
    }
    for(i=3;i<=n;i+=2){
        if(a[i]==0)
            k++;
    }
    fout<<k;
    fin.close();
    fout.close();
    return 0;
}