#include<stdio.h>
#include<stdbool.h>

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

    int N;
    int primes = 0;
    scanf("%d", &N);
    bool numbers[N];
    for(int i = 0; i<N;i++){
        numbers[i] = true;
    }

    int i = 2;
    while(i<N) {
        primes++;
        for(int j = i; j < N; j = j+i) {
            numbers[j] = false;
        }
        while(!numbers[i]) i++;
    }

    printf("%d", primes);
}