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#include <iostream>
#include <fstream>
#include <bitset>
#include <stdio.h>
#define MAX 2000003
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<MAX> v;
long n,k;
int main() {
in >> n;
for(long long i = 2; i <= n; i++) {
if(v[i] == 0) {
k++;
long long mult = i*i;
while(mult < n) {
v[mult] = 1;
mult += i;
}
}
}
out << k;
return 0;
}