#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
vector<int> table;
bool isprim[100000001];
int n;
int main(){
    int n;
    cin >> n;
    memset(isprim, true, sizeof(isprim));
    isprim[1] = false;
    for(int i = 2; i <= n; i++) {
        if(isprim[i]) {
            table.push_back(i);
        }
        for(int j = 0; j <= table.size() && i * table[j] <= n; j++) {
            isprim[i * table[j]] = false;
            if(i % table[j] == 0) {
                break;
            }
        }
    }
    cout << table.size() << endl;
    return 0;
}