#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N,i,j,nrp;
bool v[2000005];

int main()
{
    fin>>N;
    for(i=4;i<=N;i+=2)v[i]=1;
    nrp=1;
    for(i=3;i*i<=N;i+=2)
        if(v[i]==0)
        {
            for(j=i*i;j<=N;j+=2*i)
                v[j]=1;
        }
     for(i=3;i<=N;i+=2)if(v[i]==0)++nrp;
    fout<<nrp;
    return 0;
}