#include <iostream>
#include <vector>
#include <set>
using namespace std;
vector<long long> p;
set<long long> s;
bool used[500010];
void prime(int n){
	int i,j;
	for(i=2;i<=n;i++){
		used[i] = true;
	}
	for(i=2;i<=n;i++){
		if(!used[i]) continue;
		for(j=2*i;j<=n;j+=i){
			used[j] = false;
		}
	}
}

int main(){
	int i,n,cnt = 1;
	cin >> n;
	if(n==1){
		cout << 0 << endl;
		return 0;
	}
	prime(n);
	for(i=3;i<=n;i++){
		if(used[i]){
			p.push_back(i);
			s.insert(i);
		}
	}
	for(i=0;i<p.size();i++){
		if(p[i]*p[i]>n) break;
		if(s.count(p[i]*p[i] - 2)) cnt += 2;
	}
	cout << cnt << endl;
}