#include <iostream>

using namespace std;
const int MAXN = 2000000;
char c[MAXN + 1];
int main()
{
    FILE *fin, *fout;
    int n, i, j, rez;
    fin = fopen("ciur.in", "r");
    fscanf(fin, "%d", &n);
    fclose(fin);
    for (i = 2; i * i <= n; i++) {
        if (c[i] == 0) {
            for (j = i * i; j <= n; j += i) {
                c[j] = 1;
            }
        }
    }
    rez = 0;
    for (i = 2; i <= n; i++) {
        rez += 1 - c[i];
    }
    fout = fopen("ciur.in", "r");
    fprintf(fout, "%d\n", rez);
    fclose(fout);
    return 0;
}