#include <cstdio>
using namespace std;

const int NMAX = 2000010;

int N, Nr;
bool Prime[NMAX];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%i", &N);
    for(int i = 2; i <= N; ++ i) Prime[i] = 1;
    for(int i = 2; i <= N; ++ i)
        if(Prime[i])
        {
            Nr ++;
            for(int j = 2 * i; j <= N; j += i)
                Prime[j] = 0;
        }

    printf("%i\n", Nr);
}