#include <stdio.h>
#define NMAX 2000001

using namespace std;

int v[NMAX] = { 0 };

bool isPrime(int n) {
    for (int i = 2;i * i <= n;++i)
        if (n % i == 0)
            return false;
    return true;
}

int main()
{
    FILE* fin, * fout;
    fin = fopen("ciur.in", "r");
    fout = fopen("ciur.out", "w");

    int n, nr = 0;
    fscanf(fin, "%i", &n);

    for (int i = 2;i <= n;++i) {
        if (v[i] == 0)
            if (isPrime(i)) {
                ++nr;
                for (int j = i;j <= n;j += i)
                    v[j] = 1;
            }
    }
    
    fprintf(fout,"%i", nr);
    printf("%i", nr);
  
    return 0;
}