#include <fstream>

using namespace std;
const int nmax=2000001;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char c[nmax];
long long n,i,j,nr;
int main()
{
    c[0]=c[1]=1;
    fin>>n;
    for(i=2;i<=n;++i)
        if(c[i]==0)
            {nr++;

        for(j=i*i;j<=n;j+=i)
            c[j]=1;}
    fout<<nr;
    return 0;
}