#include <cstdio>

#define NMAX 2000001

using namespace std;

bool c[NMAX];

int ciur(int n)
{
    int nr = 0;

    for(int i = 2; i <= n; ++ i)
        if(c[i] == 0)
        {
            ++ nr;

            for(int j = 2 * i; j <= n; j += i)
                c[j] = 1;
        }

    return nr;
}

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

    int n;
    scanf("%d", &n);

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

    return 0;
}