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