#include <iostream>
#include <fstream>
using namespace std;
const int NMAX=2000000;
bool v[NMAX +1];
ifstream f("ciur.in");
ofstream g("ciur.out");

int ciur(int n)
{
long long i,j,nr=1;
v[0]=v[1]=1;
for(i=4;i<=n;i+=2)
    v[i]=1;
for(i=3;i<=n;i+=2)
    if(v[i]==0)
    {
    nr++;
    for(j=i*i;j<=n;j+=2*i)
    v[j]=1;
    }
return nr;
}
int main()
{
int n;
f>>n;
g<<ciur(n);
}