# include <fstream>
# include <string>
using namespace std;
int main(void){ifstream fin("ciur.in"); ofstream fout("ciur.out");
	long n,i,j,nr=1;
	char ok[2000010];
	memset (ok,1,sizeof(ok));
	fin>>n;
	for(i=3;i*i<=n;i++)
		if(ok[i]){
			j=3;
			while(i*j<=n){
				ok[i*j]=0;
				j++;
			}
		}
		for(i=3;i<=n;i+=2)
			if(ok[i]) nr++;
			fout<<nr;
			fout.close();
			fin.close();
			return 0;
}