#include <fstream>
using namespace std;
#define dim 2000001

long v[dim];



int main()
{
	long i, j, n;
	
		ifstream fin("ciur.in");
		ofstream fout("ciur.out");
	fin>>n;
	
	int f=0;
	
	for(i=2;i<=n;++i)
		if(v[i]==0)
			{
				++f;
				for(j=2*i;j<=n;j+=i)
				v[j]=1;
				
		}
				fout<<f;
				
				return 0;
		}