#include <bits/stdc++.h>

using namespace std;

int n , i;
vector < int > p , low;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    scanf("%d", &n);
    low = vector < int > (n + 1 , 0);

    for (i = 2; i <= n; ++i)
    {
        if (low[i] == 0) low[i] = i, p.push_back(i);
        for (auto &it : p)
        {
            if (it > low[i] || it * i > n) break;
            low[it*i] = it;
        }
    }

    printf("%d\n", (int)p.size());

    return 0;
}