Language: C++

#include <bits/stdc++.h>
using namespace std;

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define f first
#define s second

using ll = long long;
using ld = long double;
ll INF = LLONG_MAX;

using vi = vector<int>;
using vll = vector<ll>;
using pii = pair<int, int>;

namespace output {
	void pr(int x) { cout << x; }
	void pr(long x) { cout << x; }
	void pr(ll x) { cout << x; }
	void pr(unsigned x) { cout << x; }
	void pr(unsigned long x) { cout << x; }
	void pr(unsigned long long x) { cout << x; }
	void pr(float x) { cout << x; }
	void pr(double x) { cout << x; }
	void pr(ld x) { cout << x; }
	void pr(char x) { cout << x; }
	void pr(const char* x) { cout << x; }
	void pr(const string& x) { cout << x; }
	void pr(bool x) { pr(x ? "true" : "false"); }
	template<class T> void pr(const complex<T>& x) { cout << x; }
	
	template<class T1, class T2> void pr(const pair<T1,T2>& x);
	template<class T> void pr(const T& x);
	
	template<class T, class... Ts> void pr(const T& t, const Ts&... ts) { 
		pr(t); pr(ts...); 
	}
	template<class T1, class T2> void pr(const pair<T1,T2>& x) { 
		pr("{",x.f,", ",x.s,"}"); 
	}
	template<class T> void pr(const T& x) { 
		pr("{"); // const iterator needed for vector<bool>
		bool fst = 1; for (const auto& a: x) pr(!fst?", ":"",a), fst = 0; 
		pr("}");
	}
	
	void print() { pr("\n"); } // print w/ spaces
	template<class T, class... Ts> void print(const T& t, const Ts&... ts) { 
		pr(t); if (sizeof...(ts)) pr(" "); print(ts...); 
	}
}

using namespace output;

template<class T> struct Seg { 
	const T ID = 0; // comb(ID,b) must equal b
	T combine(T a, T b) { return max(a, b);} 
	int n; vector<T> seg;
	void init(int _n) { n = _n; seg.assign(2*n,ID);}

	void update(int p, T value) {	// set value at position p
		seg[p += n] = value;
		for (p /= 2; p; p /= 2) seg[p] = combine(seg[2*p], seg[2*p+1]);
	}
    
	T query(int l, int r) {	 // sum on interval [l, r]
		T ra = ID, rb = ID; 
		for (l += n, r += n+1; l < r; l /= 2, r /= 2) {
			if (l&1) ra = combine(ra,seg[l++]);
			if (r&1) rb = combine(seg[--r],rb);
		}
		return combine(ra,rb);
	}
};

int main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	pii p1; cin >> p1.f >> p1.s;
	pii p2; cin >> p2.f >> p2.s;
	
	if (p2.f < p1.f) swap(p1, p2);
	bool flip = p1.s > p2.s;
	if (flip) swap(p1.s, p2.s);
	
	int N; cin >> N;
	vector<pii> arr;
	F0R(i, N) {
		int x, y; cin >> x >> y;
		if (x < p1.f || x > p2.f || y < p1.s || y > p2.s) continue;
		if (flip) y = p1.s + p2.s - y;
		arr.push_back(pii {x, y});
	}

    ld res;

    if (p1.f == p2.f || p1.s == p2.s) {
        res = 100LL * (p2.f - p1.f + p2.s - p1.s) - arr.size() * 20LL - arr.size() * 10LL * (ld) M_PI;
        cout << setprecision(100) << res << endl;
        return 0;
    }

	sort(arr.begin(), arr.end(), [](const auto& lhs, const auto& rhs) {
		return (lhs.f < rhs.f) || (lhs.f == rhs.f && lhs.s < rhs.s);
	});

    map<int, int> coord_y; 
    vi yarr;
    for (pii x : arr) yarr.push_back(x.s);
    sort(yarr.begin(), yarr.end());
    F0R(i, yarr.size()) coord_y[yarr[i]] = i;

    Seg<int> seg; seg.init(yarr.size());
    for (pii p : arr) {
        int y = coord_y[p.s];
        int best = 1 + seg.query(0, y);
        seg.update(y, best);
    }

    ll best = seg.query(0, yarr.size() - 1);
    res = 100LL * (p2.f - p1.f + p2.s - p1.s) - best * 20 + 5 * best * (ld) M_PI);

    cout << setprecision(100) << res << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:123:81: error: expected ';' before ')' token
  123 |     res = 100LL * (p2.f - p1.f + p2.s - p1.s) - best * 20 + 5 * best * (ld) M_PI);
      |                                                                                 ^