lật sách

#include <iostream>
using namespace std;
int main(){
    int n, p;
    cin >> n >> p;
    if((p-1)<(n-p)) {
        if(p%2 != 0) cout<<(p-1)/2;
        else cout<<p/2;
    }
    else {
        if(n%2 != 0){
            if(p%2 == 0) cout << (n-p-1)/2;
            else cout<<(n-p+1)/2;
        }
        else{
            if(p%2 == 0) cout << (n-p)/2;
            else cout<<(n-p+1)/2;
        }
    }
}