#include<bits/stdc++.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

bool v[2000001];
int N,contor;
void ciur()
{
    int i,j;
    for(i=3;i<=N;i+=2)
    {
        for(j=i+i;j<=N;j+=i)
        {
            v[j]=1;
        }
    }
    for(i=2;i<=N;i++)
    {
        if(i>2 && i%2==0)
            v[i]=1;
        if(v[i]==0)
            contor++;
    }
}


int main()
{
    in>>N;
    ciur();
    out<<contor;
    return 0;
}