#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

const int MAX=2050005;
int n,i,j,p[MAX],cnt;

int main()
{
    fin >> n;
    for(i=2;i<=n;i++)
        if(!p[i])
        {
            cnt++;
            for(j=i*i;j<=n;j+=i)
                p[j]=1;
        }
    fout << cnt;
    return 0;
}