#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops") 
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp> 
#define int long long
#define fr(i,a,b) for(int i = a ; i <= b ; ++i)
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
#define pb push_back
#define fst first
#define snd second
using namespace __gnu_pbds;
using ordered_set =
 tree<int, null_type,less<int>,
 rb_tree_tag,tree_order_statistics_node_update>;
//find_by_order(k):returns iterator to kth element starting from 0
//order_of_key(k):returns count of elements strictly smaller than k
typedef long long ll;typedef pair<int, int> pii;
typedef vector<int> vi;typedef long double ld;
template<class T>
using min_heap = priority_queue<T,vector<T>,greater<T>>; 
template<typename T> T gcd(T a, T b){return(b?__gcd(a,b):a);}
template<typename T> T lcm(T a, T b){return(a*(b/gcd(a,b)));}
template<typename T> 
void remdup(vector<T>& v) {
	sort(all(v)); v.erase(unique(all(v)), v.end());
}
template<typename T> void re(vector<T> &v) {trav(i,v) cin >> i;}
void unsyncIO() { ios_base::sync_with_stdio(0); cin.tie(0); }
#ifdef np
#include "C:\Users\navodit\Desktop\mycodes\pr.h"
#else
#define trace(...)
#endif

#define MOD 1000000007  





void solve(){
	int n ; cin >> n ;
	int mx = 0 ;
	for(int  i = 1 ; i*i <= n ;++i ){
		mx = max(mx,i*i);
	}
	cout << mx << endl;
}
signed main() {
	unsyncIO();
	int tt =1 ;
	// cin >> tt;
	rep(i,0,tt) solve();













#ifdef np
	cout <<endl<<endl<< "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
	return 0;
}

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;

#define REP(i,e,s) for(register int i=e; i<=s; i++)
#define DREP(i,e,s) for(register int i=e; i>=s; i--)
#define ll long long
#define DE(...) fprintf(stderr,__VA_ARGS__)
#define DEBUG(a) DE("DEBUG: %d\n",a)

#define int long long

int read() {
	int x=0,f=1,ch=getchar();
	while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}
const int MOD=1e9+7,MAXN=200000+10;

int fac[MAXN],inv[MAXN];

int qpow(int a,int b) {
	int ans=1;
	while(b) {
		if(b&1) ans=(ans*a)%MOD;
		a=(a*a)%MOD;
		b>>=1;
	}
	return ans;
}

int c(int m,int n) {
	if(n==m||!m||!n) return 1;
	return ((fac[m]*inv[n]%MOD)*inv[m-n])%MOD;
}

int calc(int x_1,int y_1,int x_2,int y_2) {
	return c(abs(x_2-x_1)+abs(y_2-y_1),abs(x_2-x_1));
}

signed main() {
	int h=read(),w=read(),a=read(),b=read();
	fac[0]=1;
	REP(i,1,h+w) fac[i]=(fac[i-1]*i)%MOD;
	
	REP(i,1,h+w) inv[i]=qpow(fac[i],MOD-2);
	int ans=0;	
	REP(i,1,h-a) {
		ans=(ans+calc(1,1,b,i)*(calc(b+1,i,w,h)))%MOD;
	}
	
	printf("%lld\n",ans%MOD);
	return 0;
}