#include <bitset>
#include <fstream>
using namespace std;

bitset<2000002> comp;

int sieve(int n) {
    int ans=1;
    for(int i=3;i<=n;i+=2) {
        if(comp[i])
            continue;
        ans++;
        if(1LL*i*i<=n)
        for(int j=i*i;j<=n;j+=i)
            comp[j]=true;
    }
    return ans;
}

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin>>n;
    fout<<sieve(n);
    return 0;
}