#include <bits/stdc++.h>
using namespace std;
int Ciur[2000001];
void buildCiur(){
    for(int i = 2; i <= 2000000; ++i){
        if(Ciur[i] == 0){
            for(int j = 2 * i; j <= 2000000; j += i){
                Ciur[j] = 1;
            }
        }
    }
}
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    buildCiur();
    int n, cnt = 0;
    fin >> n;
    for(int i = 2; i <= n; ++i){
        if(Ciur[i] == 0){
            cnt ++;
        }
    }
    fout << cnt;
    return 0;
}