#include <stdio.h>
#define NMAX 2000001

using namespace std;

int v[NMAX] = { 0 };

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 = 3;i <= n;i+=2) {
        if (v[i] == 0) {
            ++nr;
            for (int j = i*i;j <= n;j += i)
                v[j] = 1;
        }
    }
    
    fprintf(fout,"%i", nr);
    printf("%i", nr);
  
    return 0;
}