#include <iostream>
#include <fstream>
#include <bitset>

#define maxN 200000002
#define int64 long long

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset <maxN/2> ciur;
int n,k;

void buildCiur()
{
    if  (n>=2) ++k;
    for (int i=3; i<=n; i+=2)
        if (!ciur[i>>1])
    {
        ++k;
        for (int64 j=1LL*i*i; j<=n; j+=i<<1)
            ciur[j>>1]=1;
    }
}

int main()
{
    fin>>n;
    buildCiur();
    fout<<k;
    return 0;
}