#include <bits/stdc++.h>

using namespace std;
bitset<2000001> a;
int main()
{
    int i, j, n, cnt;
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin >> n;
    a[0] = a[1] = 1; /// 0 si 1 nu sunt prime
    for (i=4;i<=n;i+=2)
        a[i] = 1; /// Numerele pare nu-s prime
    for (i=3;i*i<=n;i+=2)
        if (a[i]==0) /// i - prim si marchez multiplii cu 1
            for (j=i*i;j<=n;j+=(2*i)) a[j] = 1;
    cnt = 0;
    for (i=2; i<=n; i++)
        if (a[i]==0) cnt++;
    fout << cnt << "\n";
    fout.close();
    return 0;
}