#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int N=2000000;

bool c[N+1];

int main()
{
    int i,j,n,nr=0;
    cin>>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++;
    cout<<nr;
    return 0;
}