#include <bits/stdc++.h>
#define Nmax 2000005

using namespace std;

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

bool prim[Nmax];
int i,j,n;

int ciur()
{
    int k = 1;
    for(i = 3;i <= n;i += 2)
    {
        if(prim[i])
            continue;
        for(j = 3*i;j <= n;j += 2*i)
            prim[j] = true;
        k++;
    }
    return k;
}

int main()
{
    f >> n;
    g << ciur();
    return 0;
}