#include <bits/stdc++.h>

using namespace std;

bitset<2000001> a;

int main()
{
    int i,j,n,cnt;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    a[0]=1;
    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 );
    cnt = 0;

    for(i = 2 ; i <= n;i++)
        if(a[i]==0) cnt++;
        g << cnt << '\n';



    return 0;
}