#include <fstream>
using namespace std;
//ifstream fin("eratostene.in");
//ofstream fout("eratostene.out");
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int i, j, n, c ;
bool v[2000006];
int main()
{
    fin>>n;
    c=0;
    v[0]=1;v[1]=1;
    for(i=1;i*i<=2000000 ;i++)
    {
        if(v[i]==0){
            for(j=i;j<=2000000/i;j++)
                v[i*j]=1;
        }
    }
    for(i=2;i<=n;i++){
        if(v[i]==0)
            c++;
    }
    fout<<c;

    return 0;
}