#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, db = 0;
    bool *L;
    scanf("%d", &n);

    L = (bool*)calloc(n+2, sizeof(bool));

    L[0] = L[1] = false;
    for(int i = 2; i < n; ++i){
        L[i] = true;
    }

    for(int i = 2; i < n; ++i){
        if(L[i]){
            db++;
            for(int j = i*i; j < n; j = j + i){
                L[j] = false;
            }
        }
    }

    printf("%d\n", db);

    return 0;
}