#include <fstream>

using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");


bool ciur[ 20000000 ];
int n, i, d, k;
int main(){
    f >> n;
    ciur[ 1 ] = 1;
    ciur[ 0 ] = 1;
    for ( i = 2; i <= n; ++i )
        if ( ciur[ i ] == 0 )
            for( d = 2 * i; d <= n; d = d + i )
                ciur[ d ] = 1;
    for( i = 1; i <= n; ++i )if ( ciur[ i ] == 0 )k++;
    g << k;
    return 0;
}