#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);
    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;
}