#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n;
bool x[2000002];
int main()
{ in>>n;
int i,j,k=0;
    for(i=2;i<=n;i++)
            {if(x[i]==0){k++;
            for(j=i*i;j<=n;j=j+i)
                x[j]=1;}}
    out<<k;
    return 0;
}