#include <stdio.h>

using namespace std;

const int MAX = 2000050;

bool v[MAX]; int n, contor = 1;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n); fclose(stdin);
    for(int i = 3; i <= n; i += 2)
        if(!v[i])
        {
            contor++;
            for(int j = 2; i * j <= n; j++)
                v[i * j] = true;
        }
    printf("%d", contor); fclose(stdout);
    return 0;
}