#include <cstdio>
#include <cmath>

int N, nr=0;
bool v[2000010];

int main () {

    freopen("ciur.in","rt",stdin);
    freopen("ciur.out","wt",stdout);

    scanf("%d", &N);
    int n = N;
    for (int i=2; i<=n; ++i) {
        if (!v[i]) ++nr;
        for (int k=i*2; k<=n; k+=i)
            v[k] = true;

    }

    printf("%d", nr);
    return 0;
}