#include <iostream>
#include <cstdio>
#include <vector>
#define _USE_MATH_DEFINES
#include <math.h>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <stdlib.h>
#include <functional>
#include <string>
#include <array>
#include <map>
#include <queue>
#include <limits.h>
#include <set>
#include <stack>
#include <random>
#include <complex>
#include <unordered_map>
#include <nmmintrin.h>
#include <chrono>
const double EPS = 1e-8;
#define Scan(a) int a;scanf("%d", &a);
#define ScanS(a) char a[500];scanf("%s", a);
#define rep(i,s,n) for(int i = (s); (n) > i; i++)
#define REP(i,n) rep(i,0,n)
#define RANGE(x,a,b) ((a) <= (x) && (x) <= (b))
#define DUPLE(a,b,c,d) (RANGE(a,c,d) || RANGE(b,c,d) || RANGE(c,a,b) || RANGE(d,a,b))
#define INCLU(a,b,c,d) (RANGE(a,c,d) && (b,c,d))
#define PW(x) ((x)*(x))
#define ALL(x) (x).begin(), (x).end()
#define MODU 1000000007
#define bitcheck(a,b)   ((a >> b) & 1LL)
#define bitset(a,b)      ( a |= (1LL << b))
#define bitunset(a,b)    (a &= ~(1LL << b))
#define MP(a,b) make_pair((a),(b))
#define Manh(a,b) (abs((a).first-(b).first) + abs((a).second - ((b).second))
#define pritnf printf
#define scnaf scanf
#define itn int
#ifdef _MSC_VER
#define __builtin_popcount _mm_popcnt_u32
#define __builtin_popcountll _mm_popcnt_u64
#endif
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a%b);
}
template<typename A, size_t N, typename T>
void Fill(A(&array)[N], const T &val) {
	std::fill((T*)array, (T*)(array + N), val);
}

int gcd(int a, int b) {
	if (b == 0) return a;
	return gcd(b, a%b);
}
pii Dir[8] = {
	{ 0 ,1 },{ -1 ,0 },{ 1 ,0 },{ 0 ,-1 },
	{ 1 ,1 },{ 1 ,-1 },{ -1 ,1 },{ -1 ,-1 }
};


pii operator+(pii obj, pii obj2) {
	return MP(obj.first + obj2.first, obj.second + obj2.second);
}
pii operator-(pii obj, pii obj2) {
	return MP(obj.first - obj2.first, obj.second - obj2.second);
}

template<class T, class OP, class PROP>
class Lazy_Segment_Tree {//0-indexed ??????
public:
	vector<T> data, lazy;
	vector<bool> isupd;
	int n;
	Lazy_Segment_Tree(int a) :n(1) {
		while (n < a) n *= 2;
		data.resize(n * 2 - 1);
		lazy.resize(n * 2 - 1);
		isupd.resize(n * 2 - 1);
	}

	void prop(int num, int s) {
		if (isupd[num]) {
			data[num] = PROP()(data[num], lazy[num], 1, s);
			if (num < n - 1) {
				lazy[num * 2 + 1] = PROP()(lazy[num * 2 + 1], lazy[num]);
				lazy[num * 2 + 2] = PROP()(lazy[num * 2 + 2], lazy[num]);
				isupd[num * 2 + 1] = 1;
				isupd[num * 2 + 2] = 1;
			}
			lazy[num] = T();
			isupd[num] = 0;
		}
	}
	void op(int a, int b, T v, int num = 0, int base = 1) {
		int l = (num + 1 - base) * (n / base), r = l + n / base;
		prop(num, r - l);
		if (a == l && b == r) {
			isupd[num] = 1;
			lazy[num] = PROP()(lazy[num], v);
			prop(num, r - l);
		}
		else {
			int nr = (l + r) / 2;
			if (nr > a) op(a, min(b, nr), v, num * 2 + 1, base * 2);
			if (nr < b) op(max(a, nr), b, v, num * 2 + 2, base * 2);
			prop(num * 2 + 1, (r - l) / 2), prop(num * 2 + 2, (r - l) / 2);
			data[num] = OP()(data[num * 2 + 1], data[num * 2 + 2]);
		}
	}

	T query(int a, int b, int num = 0, int base = 1) {
		int l = (num + 1 - base) * (n / base), r = l + n / base;

		prop(num, r - l);

		if (a == l && b == r)
			return data[num];
		else {
			int nr = (l + r) / 2;
			T ret = T();
			if (nr > a) ret = OP()(ret, query(a, min(b, nr), num * 2 + 1, base * 2));
			if (nr < b) ret = OP()(ret, query(max(a, nr), b, num * 2 + 2, base * 2));
			return ret;
		}
	}
};


template<class T>
class ADD {
public:
	T operator ()(const T a, const T b, const int ra = 1, int rb = 1) {
		return a*ra + b*rb;
	}
};

template<class T>
class UPD {
public:
	T operator ()(const T a, const T b, const int ra = 1, int rb = 1) {
		return b;
	}
};

template<class T>
class RMQ {
public:
	T operator ()(const T a, const T b) {
		return min(a, b);
	}
};
template<class T>
class SUM {
public:
	T operator ()(const T a, const T b) {
		return a + b;
	}
};

struct N {
public:
	int num;
	N(int num) : num(num) {}
	N() :num(1000000) {}
	N operator + (const N obj) const {
		return N(obj.num + num);
	}
	N operator * (const N obj) const {
		return N(obj.num * num);
	}
	bool operator < (const N obj)const {
		return obj.num > num;
	}
};


int main() {
	int n;
	cin >> n;
	vector<int> num(n);
	REP(i, n) {
		scanf("%d", &num[i]);
	}

	int dp[101][101][11] = {};
	REP(i, n) {
		dp[i][i][num[i]] = 1;
	}
	rep(i, 1, n) {
		REP(j, n - i) {
			rep(k, 0, i) {
				dp[j][j + i][10] |= dp[j][j + k][10] & dp[j + k + 1][j + i][10];
				REP(l, 10) {
					dp[j][j + i][10] |= dp[j][j + k][l] & dp[j + k + 1][j + i][l];
					dp[j][j + i][l] |= (dp[j][j + k][l] & dp[j + k + 1][j + i][l]) | (dp[j][j + k][l] & dp[j + k + 1][j + i][10]) | (dp[j][j + k][10] & dp[j + k + 1][j + i][l]);
				}
			}
		}
	}
	cout << (dp[0][n-1][10] ? "yes" : "no") << endl;
	return 0;
}

Measured memory_bytes: 3676