#include<bits/stdc++.h>
using namespace std;

char s[2000005];

int main(){
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, cnt = 0;
    fin >> n;

    for(int i = 2; i*i <= n; ++i){
        if(s[i] != '1')
            for(int j = i + i; j <= n; j += i)
                s[j] = '1';
    }

    for(int i = 2; i <= n; ++i)
        if(s[i] != '1'){
            ++cnt;
        }

    fout << cnt << "\n";

    return 0;
}