#include <iostream>
#include <fstream>
using namespace std;
int s[2000001];
int main()
{
    ifstream fcin("ciur.in");
    ofstream fcout("ciur.out");
    int x,i;
    fcin>>x;
    for(i=2;i<=x;i++)
        s[i]=0;

    int j;
    for (i=2;i<=x;i++)
        if(i*i<=x)
        if(s[i]==0)
            for (j=2*i;j<=x;j+=i)
                s[j]=1;

    int v=0;
    for (i=2;i<=x;i++)
        if (s[i]==0)
            v++;
    fcout<<v;

    return 0;
}