#include <cstdio>
#include <cmath>

#define NMAX 2000007

using namespace std;

bool v[NMAX];
int n;

void ciur(int n){
    v[0] = v[1] = 1;
    for(int i = 4; i <= n; i += 2)
        v[i] = 1;
    int Lim = sqrt(n);
    for(int i = 3; i <= Lim; i += 2)
        if(v[i] == 0)
            for(int j = i * 2; j <= n; j += i)
                v[j] = 1;
}

int main(){
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    ciur(n);
    int Ans = 0;
    for(int i = 1; i <= n; ++i)
        Ans += !(v[i]);
    printf("%d", Ans);
    return 0;
}