#include <iostream>
#include <fstream>

using namespace std;

bool v[2000002];
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int n,i;
    int sum;
    fin>>n;
    sum=1;

    for(i=3; i<=n; i+=2) {
        if(v[i]==0) {
            //nr=i;
            ++sum;
            for( int nr=i; nr<=n; nr+=i) {
                v[nr]=1;
            }
        }
    }

    fout<<sum;

    return 0;
}