#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
short int v[2000000];

int main()
{
    int n,i,contor=0,j;
    f>>n;
    for(i=2;i<=sqrt(n);i++)
            if(v[i]==0)
                for(j=2*i;j<=n;j=j+i)
                    v[j]=1;
        for(i=2;i<=n;i++)
            if(v[i]==0)
                contor++;
        g<<contor;
    return 0;

}