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

int count(int n)
{
    int k = 0;
	char *a = (char*) calloc( n,sizeof(char) );

	int p = 2;
	while ( p*p <= n )
	{
		for ( int i=2; i*p <= n; i++ )
		    a[i*p-1] = 1;
		do p++;	while ( a[p-1] );
	}

	for ( int i=2; i<n; i++)
	    if ( !a[i-1] )
	        k++;
    return k;
}


int main()
{
    int n;

	FILE *in = fopen("ciur.in", "r");
	fscanf(in, "%d", &n);
	fclose(in);

    FILE *out = fopen("ciur.out", "w");
    fprintf( out, "%d", count(n) );
    fclose(out);
}