#include <iostream>
#include <fstream>
using namespace std;
const int N = 2000001;
bool c[N];
int main()
{
    int n,j,i,b,nr=0;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for(i=2;i*i<n;i++)
    {
        if(!c[i])
            for(j=i*i;j<=n;j+=i)
                c[j]=true;
    }
    for(i=2;i<=n;i++)
        if(!c[i]) nr++;
    fout<<nr<<"\n";
    return 0;
}