#include <stdio.h>

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

    int number;
    scanf("%d", &number);
    bool checked[2000001];
    int result = 0;

    for(int i = 2; i < number; i++){
        if(!checked[i]){
            result++;
            for(int j = i*2; j <=number; j+=i){
                checked[j] = true;
            }
        }
    }
    printf("%d",result);
    return 0;
}