#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PII pair<int, int>

#define PLI pair<LL, int>

#define ull unsigned long long

using namespace std;

const int N = 3e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

int n;

ull Pow[N];

struct segmentTree {

#define lson l,mid,rt<<1

#define rson mid+1,r,rt<<1|1

    struct info1 {

        ull hs; int len;

        info1 operator + (const info1 &rhs) {

            return info1{hs+rhs.hs*Pow[len], len+rhs.len};

        }

    } a[N<<];

    struct info2 {

        ull hs; int len;

        info2 operator + (const info2 &rhs) {

            return info2{rhs.hs+hs*Pow[rhs.len], len+rhs.len};

        }

    } b[N<<];

    void build(int l, int r, int rt) {

        if(l == r) {

            a[rt] = info1{, };

            b[rt] = info2{, };

            return;

        }

        int mid = l + r >> ;

        build(lson); build(rson);

        a[rt] = a[rt<<] + a[rt<<|];

        b[rt] = b[rt<<] + b[rt<<|];

    }

    void update(int p, int l, int r, int rt) {

        if(l == r) {

            a[rt] = info1{, };

            b[rt] = info2{, };

            return ;

        }

        int mid = l + r >> ;

        if(p <= mid) update(p, lson);

        else update(p, rson);

        a[rt] = a[rt<<] + a[rt<<|];

        b[rt] = b[rt<<] + b[rt<<|];

    }

    info1 querya(int L, int R, int l, int r, int rt) {

        if(l >= L && r <= R) return a[rt];

        int mid = l + r >> ;

        if(R <= mid) return querya(L, R, lson);

        else if(L > mid) return querya(L, R, rson);

        else return querya(L, R, lson) + querya(L, R, rson);

    }

    info2 queryb(int L, int R, int l, int r, int rt) {

        if(l >= L && r <= R) return b[rt];

        int mid = l + r >> ;

        if(R <= mid) return queryb(L, R, lson);

        else if(L > mid) return queryb(L, R, rson);

        else return queryb(L, R, lson) + queryb(L, R, rson);

    }

} seg;

int main() {

    for(int i=Pow[]=; i < N; i++) Pow[i]=Pow[i-]*;

    scanf("%d", &n);

    seg.build(, n, );

    bool flag = false;

    for(int i = ; i <= n; i++) {

        int x; scanf("%d", &x);

        int len = min(x-, n-x);

        if(len && seg.querya(x-len, x-, , n, ).hs != seg.queryb(x+, x+len, , n, ).hs)

            flag = true;

        seg.update(x, , n, );

    }

    if(flag) puts("YES");

    else puts("NO");

    return ;

}

/*

*/