#include<cstdio>
#include<bitset>

using namespace std;

const int Nmax = 2000000/2/8+1;

int N, rez;
char p[Nmax];

//(p[i>>3]&(1<<(i&7))) == 0 if 2*i + 1 is prime

int eratostene(int n) {
    int i, j, nr = 1;
    for(i = 1; ((i * i) << 1) + (i << 1) <= n; i++) {
        if((p[i >> 3] & (1 << (i & 7))) == 0) {
            for (j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1) {
                p[j >> 3] |= (1 << (j & 7));
            }
        }
    }

    for(i = 1; 2 * i + 1 <= n; ++i)
        if ((p[i >> 3] & (1 << (i & 7))) == 0)
            nr++;

    return nr;
}

int main() {

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

    scanf("%d",&N);
    rez = eratostene(N);
    printf("%d\n",rez);

    return 0;
}