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