#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define all(x) (x).begin(),(x).end()
#define foreach(u,v) for(auto (u) : (v))
#define pb push_back
#define mp make_pair
#define mt make_tuple

#define int long long 

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;

const int inf = 1e9;
const ll linf = 1LL<<60;
const ll mod = 1e9 + 7;
const double eps = 1e-9;

/*
  u = x + y, v = x - y
  d = max(|u|, |v|);
*/

signed main()
{
  int x, y, d;
  cin >> x >> y >> d;
  
  int u = x+y;
  int v = x-y;

  if(u < d) cout << 0 << endl;
  else if(d == 0) cout << 1 << endl;
  else cout << (1+d - max(0LL, d-y) - max(0LL, d-x)) << endl;  

  return 0;
}