#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
char ciur[2000005];
int main()
{
    int i,j,n,cnt = 0;
    in >> n;
    in>>n;
    for (i=2;i<=n;i++)
    {
        if(ciur[i] == 0)
        {
            for (j=i*2;j<=n;j=j+i)
                ciur[j]=1;
        }
    }
    for (i=2;i<=n;i++)
        if ( ciur[i]==0 ) cnt++;
    out << cnt;
    return 0;
}