#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC optimize(3)
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC target("sse3","sse2","sse")
#pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
#pragma GCC target("f16c")
#pragma GCC optimize("inline","fast-math","unroll-loops","no-stack-protector")
#pragma GCC diagnostic error "-fwhole-program"
#pragma GCC diagnostic error "-fcse-skip-blocks"
#pragma GCC diagnostic error "-funsafe-loop-optimizations"
#pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
//#include "ext/pb_ds/tree_policy.hpp"
//#include "ext/pb_ds/assoc_container.hpp"
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x,"r",stdin)
#define fw(x) freopen(x,"w",stdout)
#define iout(x) printf("%d\n",x)
#define lout(x) printf("%lld\n",x)
#define REP(x,l,u) for(ll x = l;x<u;x++)
#define RREP(x,l,u) for(ll x = l;x>=u;x--)
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define mst(x,a) memset(x,a,sizeof(x))
#define all(a) a.begin(),a.end()
#define PII pair<int,int>
#define PLL pair<ll,ll>
#define MP make_pair
#define sqr(x) ((x)*(x))
#define lowbit(x) (x&(-x))
#define lson (ind<<1)
#define rson (ind<<1|1)
#define se second
#define fi first
#define dbg(x) cerr<<#x<<" = "<<(x)<<endl;
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef  long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9+7;
const ll inf = 1e9+7;
const ld eps = 1e-9;
const db PI = atan(1)*4;
template<typename T>
inline int sign(const T&a) {
    if(a<0)return -1;
    if(a>0)return 1;
    return 0;
}

template<typename T,typename S>inline bool upmin(T&a,const S&b){return a>b?a=b,1:0;}
template<typename T,typename S>inline bool upmax(T&a,const S&b){return a<b?a=b,1:0;}

template<typename T> inline void in(T &x) {
    x = 0;
    T f = 1;
    char ch = getchar();
    while (!isdigit(ch)) {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (isdigit(ch))  {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    x *= f;
}

ll twop(int x) {
    return 1LL<<x;
}

template<typename A,typename B > inline void in(A&x,B&y) {
    in(x);
    in(y);
}
template<typename A,typename B,typename C>inline void in(A&x,B&y,C&z) {
    in(x);
    in(y);
    in(z);
}
template<typename A,typename B,typename C,typename D> inline void in(A&x,B&y,C&z,D&d) {
    in(x);
    in(y);
    in(z);
    in(d);
}
ll gcd(ll a,ll b){return b==0?a:gcd(b,a%b);}
namespace SOLVE {
    void main(){
    }
}
// m must be positive
template<typename T>
static T MOD(T a, T m)
{
    a %= m;
    if (a < 0)
        a += m;
    return a;
}

// a must be relatively prime to m
template<typename T>
static T inverse(T a, T m)
{
    a = MOD(a, m);
    if (a <= 1)
        return a;
    return MOD((1 - inverse(m, a) * m) / a, m);
}

const ll maxn = 1000010;
ll fac[maxn],facinv[maxn],inv[maxn];
void init(){
    fac[0] = 1;
    REP(i,1,maxn)fac[i] = i*(fac[i-1])%mod;
    facinv[maxn-1]=inverse(fac[maxn-1], mod);
    RREP(i,maxn-2,0){
        facinv[i] = facinv[i+1]*(i+1)%mod;
    }
    inv[1]=1;
    for(int i=2;i<maxn;i++)
        inv[i]=(mod-(ll)mod/i*inv[mod%i]%mod);
}

ll combi(int n,int m){
    if(n<0 || m<0 || n<m)return 0;
    return fac[n]*facinv[m]%mod*facinv[n-m]%mod;
}


ll n,m,a,b;
int main(){
    
    
    in(n,m,a,b);
    
    n--;
    m--;
    a--;
    b--;
    
    
    
    init();
    ll ans = combi(n+m, n);
    REP(i,0,b+1){
        ans -= combi(n-a+i-1,i)*combi(m-i+a,a)%mod;
    }
    ans%=mod;
    if(ans<0)ans+=mod;
    cout<<ans;
    return 0;
}


Measured memory_bytes: 23680