#include <iostream>
using namespace std;
//#define ll long long
bool ciur[2000005];

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    int n; scanf("%d", &n);

    ciur[0] = ciur[1] = true;
    int cnt = 0;
    for (int i = 2; i <= n; i++) {
        if (i <= n && ciur[i] == false)
            ++cnt;
        for (int j = 2; i * j <= n; j++)
            ciur[i * j] = true;
    }

    printf("%d", cnt);

    fclose(stdin);
    fclose(stdout);
    return 0;
}