#include<iostream>
#include<fstream>
using namespace std;
int n,i,j,a;
bool p[2000005];
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    p[1]=1;
    in>>n;
    for(i=2;i<=n;i++)
    {
        if(p[i]==0)
        {
            for(j=i+i;j<=n;j=j+i)
                p[j]=1;
        }
    }
    for(i=1;i<=n;i++)
        if(p[i]==0)
            a++;
            out<<a;
}