#include<iostream>
#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000001];
int main ()
{
    int i,N,j,s=0;
    f>>N;
    for(i=4;i<=N;i+=2)
        v[i]=1;
    for(i=3;i*i<=N;i++)
    {
        for(j=i*i;j<=N;j+=i)
            v[j]=1;
    }
    for(i=2;i<=N;i++)
        if(v[i]==0)
        s++;
    g<<s;
    return 0;
}