/*
Author: Qaseem Hasan alias Mikepayne14(Codeforces,Atcoder) 
                           qaseem_hasan_ (Codechef,HackerRank,HackerEarth)
*/


//---------------------------------------------------------
//#pragma GCC optimize "trapv"

#include <bits/stdc++.h>
using namespace std;
//---------------------------------------------------------

typedef long long int ll;
typedef unsigned long long int ull;
typedef long double ld;
typedef double db;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<char> vc;
typedef vector<vector<int>> vvi;
typedef pair<int,int> pii;
typedef vector<pair<int,int>> vpii;
typedef vector<vector<pair<int,int>>> vvpii;
typedef set<int> seti;
typedef unordered_set<int> us;
typedef unordered_set<int,greater<int>> usrev;
typedef priority_queue <int, vector<int>, greater<int>> revpq;

const int INF = (int)1e9;
const int EPS = 1e-8;
const int MOD  = 1000000007;
const ld PI = 3.14159265359;

#define acc accumulate
#define eb emplace_back
#define mii map <int,int>
#define F first
#define S second
#define MP make_pair
#define mid(s,e) (s+(e-s)/2)
#define fil(v,x) fill(all(v),x)
#define filcon(v,x) iota(all(v),x)
#define repi(n) for(int i=0;i<n;++i)
#define repj(n) for(int j=0;j<n;++j)
#define repr(n) for(int i=n-1;i>=0;--i)
#define erase(v,e) v.erase(std::remove(v.begin(), v.end(), e), v.end())
#define sqr(x) ((x)*(x))
#define MEM(a,b) memset(a, b, sizeof(a))
#define all(cont) cont.begin(), cont.end()
#define rall(cont) cont.end(), cont.begin()
#define FOREACH(it, l) for (auto it = l.begin(); it != l.end(); it++)
#define inrange(i,a,b) ((i>=min(a,b)) && (i<=max(a,b)))
#define FLSH fflush(stdout)
// #define min_all(a,b,c,d,...) min({a,b,c,d,...})
#define PRECISION(x) cout << fixed << setprecision(x)
#define FAST_IO ios::sync_with_stdio(false); cin.tie(nullptr);
#define make_unique(v) sort(all(v)); v.erase(unique(all(v)), v.end());
#define readfull(s) getline(cin,s)
#define printv(v) for(auto i:v) cout << i << " "
#define trace(x) cout<<#x<<" = { "<<x<<" }\n";
#define khatam '\n'
#define test int t; cin >> t; repi(t) {solve(); cout << khatam;}
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time__(d) \
for ( \
    auto blockTime = make_pair(chrono::high_resolution_clock::now(), true); \
    blockTime.second; \
    debug("%s: %lld ms\n", d, chrono::duration_cast<chrono::milliseconds>(chrono::high_resolution_clock::now() - blockTime.first).count()), blockTime.second = false \
)

//--------------------------------------------------------
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; } //x=min,y=item
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

template<typename T>
T lcm(T a,T b)
{
    return (a*b)/__gcd(a,b);
}

template<typename ForwardIterator,typename T>
T first_val(ForwardIterator first,ForwardIterator last,T value)
{
    auto it = std::lower_bound(first,last,value);
    return (it!=last)?(it - first) : -1;
}

template<typename ForwardIterator,typename T>
T last_val(ForwardIterator first,ForwardIterator last,T value)
{
    auto it = std::upper_bound(first,last,value);
    return ((it!=last)?((it - first)-1) : -1);
}

template <typename T> T Dis(T x1,T y1,T x2, T y2)
{return sqrt(sqr(x1-x2) + sqr(y1-y2));}

template <typename T> T Angle(T x1,T y1,T x2, T y2)
{return atan((db)(y1-y2) / (db)(x1-x2));}

int Set(int N,int pos){ return N=N | (1<<pos);}
int Reset(int N,int pos){return N= N & ~(1<<pos);}
bool Check(int N,int pos){return (bool)(N & (1<<pos));}
template< class T, class X > inline T togglebit(T a, X i) { T t=1;return (a^(t<<i));}

//--------------------------------------------------------

bool compare(const pair<int, int>&i, const pair<int, int>&j)
{
    return i.F < j.F;
}

int doubleCompare(double x, double y) {
    if (fabs(x-y) <= EPS)
        return 0;
    if(x < y)
        return -1;
    return 1;
}

int countSetBits(int n)
{
    int count=0;
    while(n>0)
    {
        count += (n&1);
        n = n>>1;
    }
    return count;
}

int getPosBit(ll n,int k)
{
    return (n&(1<<k))!=0?1:0;
}

void setPosBit(int &n,int k)
{
    n = n|(1<<k);
}

ll fast_power(int a,int x)
{
    if(x==0)
        return 1;
    else if(x==1)
        return a;
    else
    {
        ll R = fast_power(a,x>>1);
        if(!(x&1))
            return R*R;
        else
            return R*a*R;
    }
}

ll fast_power_unlocked(ll a,ll n,ll mod)
{
    ll res = 1;
    while(n > 0)
    {
        if(n&1)
        {
            res = (res*a)%mod;
        }
        a = (a*a)%mod;
        n = n >> 1;
    }
    return res;
}

ll modInverse(ll A,ll M)
{
    return fast_power_unlocked(A,M-2,M);
}

/*
bool checkPrime2(int n)
{
    int cnt=0;
    for(int i=1;i*i<=n;i++)
    {
        if(n%i == 0)
        {
            if(n/i == i)
                cnt++;
            else
                cnt += 2;
        }
    }
    if(cnt == 2)
        return true;
    else
        return false
}

bool isPrime[10001];
void createSieve(int n)
{
    MEM(isPrime,true);
    for(int i=2;i*i<=10000;i++)
    {
        if(isPrime[i])
        {
            for(int j=i*i;j<=10000;j+=i)
            {
                isPrime[j] = false;
            }
        }
    }
    if(isPrime[n])
        cout << "yes";
}*/

/*bool check_composite(ll n, ll a, ll d, int s) {
    ll x = binpower(a, d, n);
    if (x == 1 || x == n - 1)
        return false;
    for (int r = 1; r < s; r++) {
        x = (ull)x * x % n;
        if (x == n - 1)
            return false;
    }
    return true;
}

bool MillerRabinPrimeCheck(ll n){
    if (n < 2)
        return false;

    int r = 0;
    ll d = n - 1;
    while ((d & 1) == 0) {
        d >>= 1;
        r++;
    }

    for (int a : {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37}) {
        if (n == a)
            return true;
        if (check_composite(n, a, d, r))
            return false;
    }
    return true;
}*/
const int MAX_N = 64;

// int vis[MAX_N];

// int ar[MAX_N];

// vi vis(MAX_N,0);

//vvi graph(MAX_N);

void solve()
{
    string s;
    string t;
    cin >>s>>t;
    int flag=0;
    for(int i=0;i<s.size();i++)
    {
        if(s[i]!=t[i])
            flag=1;
    }
    if(flag)
        cout << "No";
    else
    {
        if(s.size()+1==t.size())
            cout << "Yes";
        else
            cout << "No";
    }
}

int main()
{
    FAST_IO;
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
//-------------------------------------------------------
        time__("Time Taken"){
        solve();
    }
}

Measured memory_bytes: 3744