#pragma region
#pragma GCC target("avx2")
#pragma GCC optimize("03")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std; typedef long double ld; typedef long long ll;
typedef unsigned long long ull;
#define endl "\n"
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define rep(i,n) for(int i=0;i<(n);i++)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define ALL(x) (x).begin(), (x).end()
constexpr int INF=1<<30; constexpr ll LINF=1LL<<60; constexpr ll mod=1e9+7; constexpr int NIL = -1;
template<class T>inline bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>inline bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
#pragma endregion
//-------------------
constexpr int MX = 5e5+3;
int n;
bool visited[MX];

vector<int> prime(int k) {
    vector<int> ans;
    for(int i=3;i<=k;i+=2) {
        if(visited[i]) continue;
        ans.push_back(i);
        for(int j=i+i; j<=k; j+=i) {
            visited[j] = true;
        }
    }
    return ans;
}

int main(){
    cin.tie(0); ios::sync_with_stdio(false); //cout << fixed << setprecision(15);
    cin >> n;

    if(n==1) {
        cout << 0 << endl;
        return 0;
    }
    auto primes = prime(n);
    map<int, int> mp;
    for(auto &e: primes) {
        mp[e]++;
        if(e > n) cout << e << endl;
    }

    int ans = 1;
    for(auto &r: primes) {
        if(mp[r*r-2]) ans += 2;
        if(r*r-2 > n) break;
    }
    cout << ans << endl;
    return 0;
}