#ifdef _MSC_VER
#define _CRT_SECURE_NO_WARNINGS
#include <windows.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

#define MY_FILE_NAME "ciur"

void read_data( int *n )
{
	FILE *f = fopen( MY_FILE_NAME".in", "r" );
	fscanf( f, "%i", n );
}

void write_response( long long response )
{
	FILE *f = fopen( MY_FILE_NAME".out", "w" );
	fprintf( f, "%lli", response );
}

void run();

int main()
{
#ifdef _MSC_VER
	unsigned int start_tick = GetTickCount();
	//time_t start_time = time( NULL );
#endif

	run();

#ifdef _MSC_VER
	//int secs = (int) (time( NULL ) - start_time);
	//printf( "***** %i secs\n", secs );
	int milis = GetTickCount() - start_tick;
	printf( "***** %i milis\n", milis );
#endif
	return 0;
}

void run()
{
	int n = 0;
	int response = 0;
	static char v[1 + 2000000];

	read_data( &n );

	v[0] = v[1] = 1; // neprime
	for ( int i = 2; i <= n; i++ ) {
		if ( !v[i] ) {
			response ++;
			for ( int j = i+i; j <= n; j += i )
				v[j] = 1;
		}
	}

	write_response( response );
}