#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<1000000>v;
int main()
{
    int n,i,j,k=0;
    fin>>n;
    v[1]=v[0]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            {
                k++;
                for(j=2*i;j<=n;j=j+i)
                    v[j]=1;
            }
    fout<<k;
    fin.close();
    fout.close();
    return 0;
}