#include <bits/stdc++.h>
#define ll long long
#define N 100000
using namespace std;
int sz[N], rev[N], tag[N], sum[N], ch[N][2], fa[N], val[N];
int n, m, rt, x;
void push_up(int x)
{
    sz[x] = sz[ch[x][0]] + sz[ch[x][1]] + 1;
    sum[x] = sum[ch[x][1]] + sum[ch[x][0]] + val[x];
}
void push_down(int x)
{
    if(rev[x])
	{
        swap(ch[x][0], ch[x][1]);
        if(ch[x][1]) rev[ch[x][1]] ^= 1;
        if(ch[x][0]) rev[ch[x][0]] ^= 1;
        rev[x] = 0;
    }
    if(tag[x])
	{
        if(ch[x][1]) 
        {
        	tag[ch[x][1]] += tag[x], sum[ch[x][1]] += tag[x];
        }
        if(ch[x][0]) 
        {
        	tag[ch[x][0]] += tag[x], sum[ch[x][0]] += tag[x];
        }
        tag[x] = 0;
    }
}
void rotate(int x, int &k)
{
    int y = fa[x], z = fa[fa[x]];
    int kind = ch[y][1] == x;
    if(y == k) 
    {
    	k = x;
    }
    else 
    {
    	ch[z][ch[z][1]==y] = x;
    }
    fa[x] = z; 
	fa[y] = x; 
	fa[ch[x][!kind]] = y;
	
    ch[y][kind] = ch[x][!kind]; 
	ch[x][!kind] = y;
	
    push_up(y); 
	push_up(x);
}
void splay(int x, int &k)
{
    while(x != k)
	{
        int y = fa[x], z = fa[fa[x]];
        if(y != k) if(ch[y][1] == x ^ ch[z][1] == y) 
        {
        	rotate(x, k);
        }
        else 
        {
        	rotate(y, k);
        }
        rotate(x, k);
    }
}
int kth(int x, int k)
{
    push_down(x);
    int r = sz[ch[x][0]]+1;
    if(k == r) 
    {
    	return x;
    }
    if(k < r) 
    {
    	return kth(ch[x][0], k);
    }
    else 
    {
    	return kth(ch[x][1], k-r);
    }
}
void split(int l, int r)
{
    int x = kth(rt, l), y = kth(rt, r+2);
    splay(x, rt); 
	splay(y, ch[rt][1]);
}
void rever(int l, int r)
{
    split(l, r);
    rev[ch[ch[rt][1]][0]] ^= 1;
}
void add(int l, int r, int v)
{
    split(l, r);
    tag[ch[ch[rt][1]][0]] += v;
    val[ch[ch[rt][1]][0]] += v;
    push_up(ch[ch[rt][1]][0]);
}
int build(int l, int r, int f)
{
    if(l > r) 
    {
    	return 0;
    }
    if(l == r)
	{
        fa[l] = f;
        sz[l] = 1;
        return l;
    }
    int mid = l + r >> 1;
    ch[mid][0] = build(l, mid-1, mid);
    ch[mid][1] = build(mid+1, r, mid);
    fa[mid] = f;
    push_up(mid);
    return mid;
}
int asksum(int l, int r)
{
    split(l, r);
    return sum[ch[ch[rt][1]][0]];
}
int main()
{
    n = 2;
    rt = build(1, n+2, 0);
    for(int i = 1; i <= n; i++)
	{
        scanf("%d", &x);
        add(i, i, x);
    }
    rever(1, n);
    printf("%d\n", asksum(1, n));
    return 0;
}