#include <iostream>
#include <fstream>

using namespace std;

const int MAXN = 2000005;

bool ciur[MAXN];
int val[MAXN];

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