#include <bits/stdc++.h>

using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool sir[2000001];
int main()
{
    long long N,i,s=0,j;
    in>>N;
    sir[1]=1;
    for(i=2; i<=N; i++)
    {
        if(sir[i]==0)
        {
            s=s+1;
            if(i*i<=N)
            {
                for(j=i+i; j<=N; j=j+i)
                    sir[j]=1;
            }
        }
    }
    out<<s;
    return 0;
}