#include <bits/stdc++.h>

using namespace std;

bool ciur[2000005];
vector<int> prime;

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin >> n;
    ciur[1] = 1;
    for(int i = 2; i <= n; ++i){
        if(!ciur[i]){
            prime.push_back(i);
            for(int j = i * i; j <= n; j += i)
                ciur[j] = 1;
        }
    }
    fout << prime.size();
    return 0;
}