#include <bits/stdc++.h>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];

int main()
{
    int n,i,j,cnt=0;
    in>>n;
    for(i=3;i<=n;i=i+2)
    {
    if(v[i]==0)
   for(j=i*i;j<=n;j=j+i)
        v[j]==1;

    }
    for(i=3;i<=n;i+=2)
      if(v[i]==0)
            cnt++;
    out<<cnt;
    return 0;
}