#include    <iostream>
#include    <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

const int NMAX = 2000005;

char prim[NMAX];

int main()
{
    int N, prime, cnt = 0;
    f >> N;
    for(int i = 2; i <= N; ++i) prim[i] = 1;
    for(int i = 2; i <= N; ++i){
        if(prim[i]){
            ++cnt;
            for(int j = i + i; j <= N; j+=i)
                prim[j] = 0;
       }
       g << cnt;
    }
    return 0;
}