Language: C++

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

// Shortcut

//#define int long long
#define endl '\n'
#define eb emplace_back
#define pb push_back
#define pob pop_back
#define mp make_pair
#define upb upper_bound
#define lwb lower_bound
#define fi first
#define se second
#define For(i, l, r) for (int i = l; i < r; i++)
#define ForE(i, l, r) for (int i = l; i <= r; i++)
#define Ford(i, r, l) for (int i = r; i > l; i--)
#define FordE(i, r, l) for (int i = r; i >= l; i--)
#define Fora(i, a) for (auto i : a)

// I/O & Debug

#define PrintV(a) for (int iiii = 0; iiii < a.size(); iiii++) cout << a[iiii] << ' ';
#define PrintVl(a) for (int iiii = 0; iiii < a.size(); iiii++) cout << a[iiii] << endl;
#define PrintA(a, n) for (int iiii = 0; iiii < n; iiii++) cout << a[iiii] << ' ';
#define PrintAl(a, n) for (int iiii = 0; iiii < n; iiii++) cout << a[iiii] << endl;
#define Ptest(x) return cout << x, 0;
#define gl(s) getline(cin, s);
#define setpre(x) fixed << setprecision(x)
/*
#define debug(args...){ string _sDEB = #args; replace(_sDEB.begin(), _sDEB.end(), ',', ' '); stringstream _ssDEB(_sDEB); istream_iterator<string> _itDEB(_ssDEB); DEB(_itDEB, args); }
void DEB(istream_iterator<string> it) {}
template<typename T, typename... Args>
void DEB(istream_iterator<string> it, T a, Args... args){
    cout << *it << " = " << a << endl;
    DEB(++it, args...);
}
*/

// Functions

//#define isvowel(a) (a == 'a' || a == 'e' || a == 'i' || a == 'o' || a == 'u')
#define bend(a) a.begin(), a.end()
#define rbend(a) a.rbegin(), a.rend()
#define mset(a) memset(a, 0, sizeof(a));
#define mmset(a) memset(a, 0x3f, sizeof(a));
//mt19937 rando(chrono::steady_clock::now().time_since_epoch().count());

// Data Structure

#define pque priority_queue
#define mts multiset
typedef long long ll;
typedef long double ld;
typedef vector <int> vi;
typedef vector <ll> vll;
typedef vector <ld> vld;
typedef vector <string> vs;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
typedef vector <vi > vvi;
typedef vector <vll > vvll;
typedef vector <pii > vpii;
typedef vector <pll > vpll;

const int N = 2e5 + 5, mod = 1e9 + 7, inf = 1e9 + 7;

int n, m, a, b;
int fac[N], inv[N];
 
int binpow(int a, int m){
    int res = 1, now = a;
    for (; m; m >>= 1, now = (now * now) % mod){
    	if (m & 1){
    		res = (res * now) % mod;
    	}
    }
    return res;
}
 
int C(int n, int k){
	return (((fact[n] * inv[k]) % mod) * inv[n - k]) % mod;
}

signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
	cin >> n >> m >> a >> b;
	fac[0] = 1;
	for (int i = 1; i < N; i++){
		fac[i] = (fac[i - 1] * i) % mod;
	}
	for (int i = 0; i < N; i++){
		inv[i] = binpow(fac[i], mod - 2);
	}
	int ans = 0, t;
	int x = n - a - 1, y = b;
	while (x >= 0 && y <= m - 1){
		t = C(x + y, y);
		t = t * C(n + m - x - y - 2, m - y - 1);
		ans = (ans + t) % mod;
		x--;
		y++;
	}
	cout << ans;
}

/*
==================================+
INPUT:                            |
------------------------------    |

------------------------------    |
==================================+
OUTPUT:                           |
------------------------------    |

------------------------------    |
==================================+
*/

Compiler output:
a.cc: In function 'int C(int, int)':
a.cc:83:19: error: 'fact' was not declared in this scope; did you mean 'fac'?
   83 |         return (((fact[n] * inv[k]) % mod) * inv[n - k]) % mod;
      |                   ^~~~
      |                   fac