#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1e2 + 10;
const int mod = 998244353;
int dp[N][N][2];
int x,y,p,q;
void bfs() {
	queue<pair<pair<int,int>,int>>c;
	c.push({{x,y},0});
	dp[x][y][0]=0;
	while (!c.empty()) {
		int nowx=c.front().first.first;
		int nowy=c.front().first.second;
		int flag=c.front().second;
		c.pop();
		for (int i=nowx; i>=0; i--) {
			for (int j=nowy; j>=0; j--) {
				if ((i+j<=p)&&(nowx-i+q>=nowy-j||nowx-i==0)) {
					if (dp[x-nowx+i][y-nowy+j][flag^1]>dp[nowx][nowy][flag]+1) {
					//	cout<<"对岸是："<<flag<<"当前岸上的羊："<<nowx<<"当前岸上的狼"<<nowy<<"转移的羊："<<i<<"转移的狼:"<<j<<"转移后的羊:"<<x-nowx+i<<"转移后的狼"<<y-nowy+j<<"\n";
						dp[x-nowx+i][y-nowy+j][flag^1]=dp[nowx][nowy][flag]+1;
						c.push({{x-nowx+i,y-nowy+j},flag^1});
					}
					
				}
			}
		}
	}
}
void solved() {
	cin>>x>>y>>p>>q;
	for (int i=0; i<=100; i++) {
		for (int j=0; j<=100; j++) {
			for (int k=0; k<=1; k++) {
				dp[i][j][k]=1e18;
			}
		}
	}
	bfs();
	int minn=1e18;
	for (int i=0; i<=y; i++) {
		minn=min(dp[x][i][1],minn);
	}
	if (minn>=1e18) {
		cout<<"-1\n";
	} else {
		cout<<minn<<"\n";
	}
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	int t = 1;
	// cin>>t;
	while (t--) {
		solved();
	}
}
————————————————

                            版权声明：本文为博主原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。
                        
原文链接：https://blog.csdn.net/hanghang20030820/article/details/140839351

answer.code:61:1: error: extended character — is not valid in an identifier
   61 | ————————————————
      | ^
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:61:1: error: extended character — is not valid in an identifier
answer.code:63:77: error: extended character 。 is not valid in an identifier
   63 |                             版权声明：本文为博主原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。
      |                                                                             ^
answer.code:61:1: error: ‘————————————————’ does not name a type
   61 | ————————————————
      | ^~~~~~~~~~~~~~~~