#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstring>

struct node{
	
    int data,rev,sum;
    node *son[2],*pre;
    bool judge();
    bool isroot();
    void pushdown();
    void update();
    void setson(node *child,int lr);
    
}lct[2];

int top,a,b;

node *getnew(int x){
	
    node *now=lct+ ++top;
    
    now->data=x;
    now->pre=now->son[1]=now->son[0]=lct;
    now->sum=0;
    now->rev=0;
    
    return now;
}

bool node::judge(){
	
	return pre->son[1]==this;
}

bool node::isroot(){
	
    if(pre==lct){
    	
    	return true;
	}
    
    return !(pre->son[1]==this||pre->son[0]==this);
}

void node::pushdown(){
	
    if(this==lct||!rev){
    	
    	return;
	}
	
    std::swap(son[0],son[1]);
    
    son[0]->rev^=1;
    son[1]->rev^=1;
    
    rev=0;
}

void node::update(){
	
	sum=son[1]->sum+son[0]->sum+data;
}

void node::setson(node *child,int lr){
	
    this->pushdown();
    child->pre=this;
    son[lr]=child;
    this->update();
}

void rotate(node *now){
	
    node *father=now->pre,*grandfa=father->pre;
    
    if(!father->isroot()){
    	
    	grandfa->pushdown();
	} 
	
    father->pushdown();now->pushdown();
    
    int lr=now->judge();
    
    father->setson(now->son[lr^1],lr);
    
    if(father->isroot()){
    	
    	now->pre=grandfa;
	}
	
    else{
    	
    	grandfa->setson(now,father->judge());
	}
	
    now->setson(father,lr^1);
    father->update();now->update();
    
    if(grandfa!=lct){
    	
    	grandfa->update();
	}
}

void splay(node *now){
	
    if(now->isroot()){
    	
    	return;
	}
	
    for(; !now->isroot(); rotate(now))
    
    if(!now->pre->isroot())
    
    now->judge()==now->pre->judge()?rotate(now->pre):rotate(now);
}

node *access(node *now){
	
    node *last=lct;
    
    for(;now!=lct;last=now,now=now->pre){
    	
        splay(now);
        
        now->setson(last,1);
    }
    
    return last;
}

void changeroot(node *now){
	
    access(now)->rev^=1;
    
    splay(now);
}

void connect(node *x,node *y){
	
    changeroot(x);
    
    x->pre=y;
    
    access(x);
}

void cut(node *x,node *y){
	
    changeroot(x);
    
    access(y);
    
    splay(x);
    
    x->pushdown();
    x->son[1]=y->pre=lct;
    x->update();
}

int query(node *x,node *y){
	
    changeroot(x);
    
    node *now=access(y);
    
    return now->sum;
}

int main()
{
	
    scanf("%d%d",&a,&b);
    
    node *A=getnew(a);
    node *B=getnew(b);
	
        connect(A,B);
    
        cut(A,B);
    
        connect(A,B);
        
    printf("%d",query(A,B)); 
    
    return 0;
}

免责声明:这不是我自己写的 但是很酷