#include <fstream>
#define max 2000000
#include <bitset>

using namespace std;

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    bitset<max>v;
    int n,i,j,k=1;
    fin>>n;
    for(i=4;i<=n;i+=2)
        v[i]=1;
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
        {
            k++;
            for(j=i*i;j<=n;j=j+2*i)
                v[j]=1;
        }
    fout<<k;
    return 0;
}