/*#include <iostream>
#include <fstream>
using namespace std;
long long i,j,prime,n;
bool Prim[2000001];
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    f>>n;
    prime=1;
    for (i=2;i<=n;i+=2)
    {
        Prim[i]=true;
    }
    for (i=3;i<=n;i+=2)
    {

        if (Prim[i]==false)
        {
            cout<<i;
            prime++;
            for (j=i+i;j<=n;j=j+i)
            Prim[j]=true;
        }
    }
    g<<prime;
}
*/
#include <stdio.h>

int N, cnt;
char prim[2000005];

int main(void)
{
    int i, j;

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

    scanf("%d", &N);
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

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

    return 0;
}