#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, cnt;
char a[2000005];

int main()
{
    fin >> n;
    for(int i = 2; i * i <= n; ++i)
        for(int j = 2; j <= n / i; ++j)
            a[i * j] = 1;
    for(int i = 2; i <= n; ++i)
        if(a[i] == 0)
            cnt++;
    fout << cnt;
    return 0;
}