#include<fstream>
#include<vector>
#include<algorithm>
#include<cmath>

using namespace std;
fstream f("ciur.in");
ofstream g("ciur.out");
unsigned long n;


int getPrimes()
{
std::vector<bool> vec(n);
std::fill( vec.begin(), vec.end(), true );
for(unsigned long i=2;i<sqrt(n);i++){
if(vec[i]){
for(unsigned long j=pow(i,2);j<=n;j+=i){
vec[j]=false;
}
}
}

int result =0;
for(unsigned long i=2;i<n;i++){
if(vec[i]) result++;
}
return result;
}

int main()
{
f>>n;
g<<getPrimes();

return 0;
}