#include <cstdio>
#include <vector>
#include <bitset>

#define Nmax 2000005

using namespace std;

bitset<Nmax> ciur;
int N,nrp = 1;

void sieve()
{
    for(int i = 3; i <= N; i += 2)
        if(ciur[i] == 0){
            ++nrp;
            for(int j = 3; i*j <= N; j += 2)
                ciur[i*j] = 1;
        }
    printf("%d\n",nrp);
}

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

    scanf("%d",&N);
    sieve();

    return 0;
}