反思:自己思考的不仔细……(ŎдŎ;) ,该打该打
#include<bits/stdc++.h>
#define rep(i,s,t) for(int i = (int)(s); i <= (int)(t); i++)
#define rev(i,t,s) for(int i = (int)(t); i >= (int)(s); i--)
#define pb(x) push_back(x)
#define all(x) x.begin(),x.end()
#define sz(x) (int)(x).size()
using namespace std;
typedef long long ll;
const int mod = 1e9+7;
const double PI = 4*atan(1.0);
const int maxn = 1e5+5;
const int INF = 0x3f3f3f3f;
int vis[maxn];
int main()
{
#ifdef LOCAL_FILE
freopen("in.txt","r",stdin);
#endif // LOCAL_FILE
ios_base::sync_with_stdio(0);
cin.tie(0),cout.tie(0);
ll n,k;
ll ans = 0;
cin>>n>>k;
if(n>=k-1)
{
if(k%2 == 0)
ans = k/2-1;
else
ans = k/2;
}
else
{
if((2*n>=k+1)) //这个地方要把奇数和偶数的情况都确定好,不要像我比赛时写的只满足奇数……
ans = (2*n-k-1)/2+1;
else
ans = 0;
}
cout<<ans<<endl;
return 0;
}