#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N,cnt,i,j;
char prim[2000005];

int main(void)
{
    fin>>N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i]){
            cnt++;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

    fout<<cnt;


    return 0;
}