#include <bits/stdc++.h>
using namespace std;
#define set _set

const int maxn = 1000000000;
char p[maxn / 16 + 1];

void set(int x) {
    x >>= 1;
    p[x / 8] |= '\1' << (x % 8);
}

bool get(int x) {
    x >>= 1;
    return !((p[x / 8] >> (x % 8)) & 1);
}

void build() {
    for (int i = 3; i * i < maxn; i += 2) {
        if (!get(i))
            continue;
        for (int j = i * i; j < maxn; j += (i << 1)) {
            set(j);
        }
    }
}

bool is_prime(int x) {
    if (x == 2) return true;
    if ((x & 1) == 0) return false;
    return get(x);
}

void solve() {
    int primes = 0;
    for (int i = 1; i < maxn; ++i)
        primes += is_prime(i);
    cout << primes << '\n';
}

signed main() {
    build();
    solve();
}