#include <iostream>
#include <fstream>
using namespace std;

int main()
{ifstream f("ciur.in");
ofstream g("ciur.out");
    int N,i,j,cont;
    char v[2000009];
    f>>N;
    for (i=1;i<N;i=i+2)
        v[i]=1;
    cont=1;

    for (i=3;i<N;i+=2)
        {if (v[i]==1)
        cont++;
        for (j=i*i;j<N;j=j+i)
            v[j]=0;}
        g<<cont;
    return 0;
}