#include <fstream>

using namespace std;

ifstream F ("eratostene.in");
ofstream G ("eratostene.out");

int n,i,ciur[2000003],j,k;
int main()
{
    F>>n;

    ciur[1]=1;
    ciur[0]=1;
    for ( i=2;i*i<=n;i++ )
        if ( !ciur[i] )
            for ( j=i*i;j<=n;j+=i )
                ++ciur[j];

    for ( i=1;i<=n;i++ )
        if ( !ciur[i] )
            ++k;

    G<<k;
    return 0;
}