#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int i,j,m,n,rs=1;
bool t[1100000];

int main()
{
    fin>>n;
    for (i=1;((i*i)<<1)+(i<<1)<=n;i++)
        if (t[i]==0)
        for (j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
        t[j]=1;
    for (i=1;i*2+1<=n;i++)
        if (t[i]==0) rs++;
    fout<<rs;
    return 0;
}