#include <fstream>
using namespace std;
ifstream fin("densitate.in");
ofstream fout("densitate.out");
bool v[2000004];
int s,i,j,q,n,a,b;
int main()
{
    fin>>n;
    v[0]=v[1]=0;
    for(int i=2;i<=n;i++)
        if(v[i]==0)
        {
            s++;
            for(j=i;j*i<=n;j++)
                v[i*j]=1;
        }
    fout<<s;
    return 0;
}