#include <fstream>
#define NMAX 2000002

using namespace std;

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

bool Prim[NMAX];

int main()
{
    int N,i,j;
    in>>N;
    for(i=3;i*i<=N;i+=2)
        if(!Prim[i])
        for(j=i*i;j<=N;j+=i)
            Prim[j] = 1;
    int K=1;
    for(j=3;j<=N;j+=2)
        if(!Prim[j])
            K++;
    out<<K;
    return 0;
}