/*#include<iostream>
#include<fstream>
char a[1000000],b[1000000];
using namespace std;
int main(void)
{
	long long i,j,n,terminat=0,/*a[700000],b[700000],*//*e,nrdiv=1,putere,maxd,min,contor=0;
	
	fstream f,g;
	f.open("ciur.in",ios::in); 
	g.open("ciur.out",ios::out);
	
	f>>n;
	for (i=0;i<(n-1)/2;i++)
		a[i]=2*i+3;
	
	b[0]=2;j=0;
	while (!terminat)
	{
		for (i=0;i<(n-1)/2;i++)
			if (a[i]%b[j]==0)
				a[i]=0;
		for (i=0;a[i]==0;i++);
		if (i<(n-1)/2)
			{j++; b[j]=a[i];}
		else
		terminat=1;
	}
g<<j+1;
	

}
	*/
#include<iostream>
#include<fstream>
#include <stdio.h>
using namespace std;
int N, cnt;
char prim[2000005];
int main(void)
{
    int i,j;
    fstream f,g;
    f.open("ciur.in", ios::in);
    g.open("ciur.out", ios::out);

    f>>N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

    g<<cnt;
}