#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;
    if(n >= 2)
        cnt++;
    for(int i = 4; i <= n; i += 2)
        ciur[i] = 1;
    for(int i = 3; i <= n; i += 2){
        if(!ciur[i]){
            cnt++;
            for(int j = i * i; j <= n; j += 2 * i){
                if(j <= 0)
                    break;
                ciur[j] = 1;
            }
        }
    }
    fout << cnt;
    return 0;
}