#include <fstream>
#include <bitset>
#include <iostream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<2000000> ciur;
int main() {
    int n, cnt = 0;
    in>>n;

    for (int i = 4; i <= n; i += 2)
        ciur[i] = true;
    if (n == 1){
        out<<"0\n";
        return 0;
    }
    if (n == 2){
        out<<"1\n";
        return 0;
    }
    cnt = 1;
    bool capped = false;
    for (int i = 3; i <= n; i += 2) {
        if (i%1001 == 0) cout<<i<<"\n";
        if (i*i > 2000000)
            capped = true;
        if (!ciur[i]) {
            cnt++;
            if (!capped)
                for (int j = i * i; j <= n; j += i) {
                         ciur[j] = true;
            }
        }
    }
    out<<cnt<<"\n";
    return 0;
}