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