#include <iostream>
#include <fstream>

const int MAXN = 2e6;

using namespace std;

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

bool ciur[MAXN + 1];
int n,cnt;

int main()
{
    in>>n;
    for(int i = 2; i <= n; i++)
        v[i] = true;
    for(int i = 2; i <= n; i++){
        if(v[i]){
            cnt++;
            for(int j = i + i; j <= n; j += i)
                v[j] = false;
        }
    }
    out<<cnt;
    return 0;
}