#include <stdio.h>

long int N, nr = 0;
char V[2000001];

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

    scanf("%ld", &N);

    V[0] = V[1] = 1;

    for (int i = 2; i < N; i++) {
        if (V[i] == 0) {
            for (int j = 2 * i; j <= N; j += i) {
                V[j] = 1;
            }
        }
    }

    for (int i = 1; i <= N; i++) {
        nr += 1 - V[i];
    }

    printf("%ld", nr);

    return 0;
}