#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;
    for (i=4;i<=n; i+=2)
        a[i] =1;
    for (i=3;i*i<=n;i+=2)
        if (a[i]==0)
            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;
}