#include <fstream>
#include <bitset>

using namespace std;

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

int n,i,j,k;
bitset <2000003> ciur;
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]=1;

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

    G<<k;
    return 0;
}