#include <iostream>
#include <fstream>
#include <math.h>
#define inFile "ciur.in"
#define outFile "ciur.out"

using namespace std;

bool prim[2000001];

int main()
{
    int n,s=1,i,j;

    ifstream fin(inFile);
    fin>>n;
    fin.close();

    for(i=3;i<=n;i+=2)
    {
        if(prim[i]==0)
        {
            s++;
            for(j=i*3;j<=n;j+=i*2)
                prim[j]=1;
        }
    }

    ofstream fout(outFile);
    fout<<s;
    fout.close();
}