#include <stdio.h>

using namespace std;

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

    int N = 0, k = 0;
    char p[2000000];

    scanf("%d", &N);

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

    printf("%d\n", k);

    return 0;
}