Problem:
Score : 200 points

Problem Statement

There are N + 1 squares arranged in a row, numbered 0, 1, ..., N from left to right.

Initially, you are in Square X.
You can freely travel between adjacent squares. Your goal is to reach Square 0 or Square N.
However, for each i = 1, 2, ..., M, there is a toll gate in Square A_i, and traveling to Square A_i incurs a cost of 1.
It is guaranteed that there is no toll gate in Square 0, Square X and Square N.

Find the minimum cost incurred before reaching the goal.

Constraints

1 \leq N \leq 100

1 \leq M \leq 100

1 \leq X \leq N - 1

1 \leq A_1 < A_2 < ... < A_M \leq N

A_i \neq X

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N M X
A_1 A_2 ... A_M

Output

Print the minimum cost incurred before reaching the goal.

Sample Input 1

5 3 3
1 2 4

Sample Output 1

1

The optimal solution is as follows:

First, travel from Square 3 to Square 4. Here, there is a toll gate in Square 4, so the cost of 1 is incurred.

Then, travel from Square 4 to Square 5. This time, no cost is incurred.

Now, we are in Square 5 and we have reached the goal.

In this case, the total cost incurred is 1.

Sample Input 2

7 3 2
4 5 6

Sample Output 2

0

We may be able to reach the goal at no cost.

Sample Input 3

10 7 5
1 2 3 4 6 8 9

Sample Output 3

3

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#pragma warning(disable:4996)
#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ull = unsigned long long;
#define FOR(i, a, b) for (ll i = (ll)(a); i<(ll)(b); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(a) begin(a), end(a)
#define TPL template
#define TNM typename

TPL<TNM K, TNM V> using umap = unordered_map<K, V>;
TPL<TNM K, TNM V> using uset = unordered_set<K, V>;

TPL <class T = int> inline T IN() { T x; cin >> x; return x; }
TPL<class T> inline void OUT(const T &x) { cout << x << "\n"; }
void YESNO(bool c) { OUT(c ? "YES" : "NO"); };
void YesNo(bool c) { OUT(c ? "Yes" : "No"); };
void bOUT(bool c, string s, string t) { OUT(c ? s : t); }
struct pre_ { pre_() { cin.tie(nullptr); ios::sync_with_stdio(false); /*cout << fixed << setprecision(6);*/ } } pre__;

TPL<TNM V, TNM H> void resize(vector<V>& v, const H h) { v.resize(h); }
TPL<TNM V, TNM H, TNM ... T> void resize(vector<V>& v, const H& h, const T ... t) { v.resize(h); for (auto& _v : v) resize(_v, t ...); }
TPL<TNM V, TNM T> void fill(V& x, const T& val) { x = val; }
TPL<TNM V, TNM T> void fill(vector<V>& vec, const T& val) { for (auto& v : vec) fill(v, val); }
TPL<TNM T> vector<T> make_v(size_t a) { return vector<T>(a); }
TPL<TNM T, TNM... Ts> auto make_v(size_t a, size_t b, Ts... ts) { return vector<decltype(make_v<T>(b, ts...))>(a, make_v<T>(b, ts...)); }

TPL<TNM T> using vec2 = decltype(make_v<T>(0, 0));
TPL<TNM T> using vec3 = decltype(make_v<T>(0, 0, 0));
TPL<TNM T> using vec4 = decltype(make_v<T>(0, 0, 0, 0));
TPL<TNM T> using vec5 = decltype(make_v<T>(0, 0, 0, 0, 0));

int main(void) {
	int N, M, X;
	cin >> N >> M >> X;
	vector<int> A(M);

	REP(i, M) {
		A[i] = IN();
	}

	vector<bool> F(N + 1, false);
	REP(i, M) {
		F[A[i]] = true;
	}

	int ansR = 0;
	for (int i = X + 1; i <= N; ++i) {
		if (F[i])ansR++;
	}

	int ansL = 0;
	for (int i = X - 1; i >= 0; --i) {
		if (F[i])ansL++;
	}

	OUT(min(ansL, ansR));

	return 0;
}