#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) for(int i = (n) - 1; (i) >= 0; --i)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD LL(1e9 + 7)
#define INF 100000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;


int main() {
	int a, b, s; cin >> a >> b >> s;
	int ans = 0;
	if (a == 0) {
		ans = min(2 * s, abs(b - s) + s + 1);
	}
	else {
		if (a >= b) {
			if(a < s) ans = 2 * s - a;
			else ans = a;
		}
		else {
			if(b > s) ans = min(2 * s - a, b);
			else ans = min(2 * s - a, 2 * s - b);
		}
	}
	cout << ans << endl;
	return 0;
}