#include <fstream>
#include <math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

unsigned int v[2000001];
int main()
{
    unsigned int N,i,j,s;
    double x=sqrt(N);
    f>>N;
    for(i=4;i<=N;i+=2)
        v[i]=1;
    for(i=3;i<=x;i+=2)
        for(j=i*i;j<=N;j+=2*i)
            v[j]=i;
    for(s=0,i=2;i<=N;i++)
        if(!v[i])
            s++;
    g<<s;
}