#include <iostream>
#include <fstream>
using namespace std;
bool v[2000001];
ifstream f("ciur.in");
ofstream g("ciur.out");
void ciur(int n)
{
    int i, j;
    v[0] = v[1] = 1;
    for(i = 4; i * i <= n; i += 2)
        v[i] = 1;
    for(i = 3; i * i <= n; i += 2)
        if(v[i] == 0)
            for(j = i * i; j <= n; j += 2 * i)
                v[j] = 1;
}
int main()
{
    int n, nr = 0;
    f >> n;
    ciur(n);
    if(n > 2)
        nr = 1;
    for(int i = 3; i <= n; i += 2)
        if(v[i] == 0)
            nr++;
    g << nr;
    return 0;
}