#include <bits/stdc++.h>

using namespace std;

bool ciur[2000005];

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