#include<stdio.h>
using namespace std;
#define M 2000001

int f[M], N;


void ciur()
{
    int i, j, nr = 0;

    scanf("%d", &N);

    for(i = 2; i <= N; i++)
        if(f[i] == 0)
        {
            nr++;

            for(j = i + i; j <= N; j += i)
                    f[j] = 1;
        }

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

}


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

    ciur();

    fclose(stdin);
    fclose(stdout);

    return 0;
}