#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define srep(i,l,r) for(ll i=l;i<=r;i++)
#define irep(i,r,l) for(ll i=r;i>=l;i--)
using ll = long long;
using ld = long double;
constexpr ll mod = 998244353ll;
#define vout(v) for(auto i :v) cout<<i<<" ";
#define INF 9223300000000000000ll
#define Winf 5e12
#define nl "\n"
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define vl vector<ll>
#define pb push_back

#define vc vector<char>
#define vb vector<bool>
#define uniq(x) sort((x).begin(),(x).end());(x).erase(unique((x).begin(),(x).end()),(x).end())
#define eb emplace_back



void no(void) { cout<<"No"<<nl;}
void yes(void) {cout<<"Yes"<<nl;}
void yn(bool a) {
    cout<<(a ? "Yes":"No")<<nl;
}


vector<ll> dx={-1,0,1,0,1,1,-1,-1};
vector<ll> dy={0,-1,0,1,-1,1,-1,1};

bool isin(ll i,ll j,ll h,ll w) {
    if(i<0 || i>=h || j<0 || j>=w) return false;
    return true;
}

template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}


template<class T>T vecmax(const vector<T>&v){return *max_element(all(v));}
template<class T>T vecmin(const vector<T>&v){return *min_element(all(v));}

ll safemod(ll num,ll rule) {
    return (num%rule+rule)%rule;
}
//alias ojb='oj-bundle -I /home/leal/beginner/atc/library'


int main() {
    ll n; cin>>n;
    vl a(n+1);
    rep(i,n) cin>>a[i+1];
    //f(0)=-1<0
    ll high=0;
    ll rem;
    srep(i,1,n) {
        if(a[i]!=0) {
            chmax(high,n+1-i);
            rem=i;
            break;
        }
    }
    if(high==0) {
        no();
        return 0;
    }
    if(a[rem]>0) {
        yes();
        return 0;
    }
    else {
        if(high%2==1) yes();
        else no();
    }
}