#include <iostream>

using namespace std;

bool prime[2000002];

int main()
{
    int i, j, n, cnt = 0;

    FILE *in, *out;
    in = fopen("ciur.in", "r");
    out = fopen("ciur.out", "w");
    fscanf(in, "%d", &n);
    for (i = 2; i*i <= n; i++){
        if (prime[i] == 0){
            for (j = i*i; j <= n; j += i){
                prime[j] = 1;
            }
        }
    }
    for (i = 2; i <= n; i++){
        if (prime[i] == 0){
            cnt++;
        }
    }
    fprintf(out, "%d", cnt);
    return 0;
}