#include<iostream>
#include<cmath>
#include<iomanip>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<vector>
#include<utility>

#define ll long long
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
using namespace std;

void Fast_IO(){
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
}





void solve(){
  ll a,b,c; cin>>a>>b>>c;
  ll even_seats = ((max(a,b)) - (min(a,b)))/2;
//   cout<<even_seats;
  if(a%2==0) even_seats +=1;
  if(b%2 == 0 && a%2 != 0) even_seats+=1;
  cout<<even_seats;




}

int main(){
    Fast_IO();
int t =1;
//cin>>t;
while(t--){
solve();
}
return 0;
}