#include <iostream>
#include <fstream>

using namespace std;

bool v[2000005];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    long long i,j,x,cnt=1;
    f>>x;
v[1]=1;
  for(i=2;i<=x;i++)
       if(v[i]==0)
       for(j=2*i;j<=x;j=j+i)
            v[j]=1;

for(i=3;i<=x;i=i+2)
     if(v[i]==0)
        cnt++;


g<<cnt;
    return 0;

}