1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
#include <bits/stdc++.h>
using ll = long long;
using sz = size_t;
using namespace std;

// make the code less c++-readable:
template<class T> using v = vector<T>; 
template<class T> using vv = v<v<T>>; 
using vi = v<int>; using vll = v<ll>; using vvi = vv<int>; using vvll = vv<ll>;

// hai loading utilities
#define $T template<class T>
#define $Ts template<class... T>
$T T Load() { T v; cin >> v; return v; }
$T auto Loads(int n) { v<T> v; v.reserve(n); while(n--) v.emplace_back(Load<T>()); return v; }
$T auto Loads() { return Loads<T>(Load<int>()); }
template<class T, int N> auto Loada() { array<T, N> a; for (T& v: a) v = Load<T>(); return a; }
$Ts auto Cols(int rows) { tuple<v<T>...> t; while(rows--) [&]<sz... I>(index_sequence<I...>){(std::get<I>(t).push_back(Load<T>()), ...);}(index_sequence_for<T...>{}); return t; }
//$Ts auto Rows(int rows) { v<tuple<T...>> v; while(rows--) { v.emplace_back(Load<T>()...); } return v; } bugged :(
struct _aIV { $T operator vector<T>() { return Loads<T>(n); } sz n; };
struct _aI { $T operator T() { return Load<T>(); } _aIV operator()(sz n) { return {n}; } }; static inline _aI $;  /* int N = $;  vi Y = $(N); */
#define MAKE_LOADER(T, alias) \
  T alias() { return Load<T>(); }   /* int x = Int(); */\
  auto alias##s() { return Loads<T>(); }   /* vector<> xs = Ints(); */\
  auto alias##s(int n) { return Loads<T>(n); }   /* vector<> xs = Ints(7); */\
  template<int N> auto alias##a() { return Loada<T, N>(); }   /* array<> xs = Inta<7>();  */\
// line intentionally left blank
MAKE_LOADER(int, Int)
MAKE_LOADER(long long, LL)
MAKE_LOADER(char, Char)
MAKE_LOADER(string, String)
// kthxbye


void test() {
    
    const ll N = $;
    const int M = $;
    const ll S = $;
    
    unordered_set<ll> zajęte;
    vector<ll> kandydaty;
    
    for (int i = 0; i < M; ++i) {
        const ll l = $;
        const ll r = $;
        
        if (l > 1) kandydaty.push_back(l-1);
        if (r < N) kandydaty.push_back(r+1);
        zajęte.insert(l);
        zajęte.insert(r);
    }
    
    sort(kandydaty.begin(), kandydaty.end(), [&](const ll c1, const ll c2) {
        return tuple(abs(c1 - S), c1) < tuple(abs(c2 - S), c2);
    });
    
    for (const ll k : kandydaty) {
        if (!zajęte.contains(k)) {
            cout << k << endl;
            return;
        }
    }
}

int main() {
    test();
    return 0;
}