import java.util.Scanner;

public class No_103 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt();
		int y = sc.nextInt();
		int d = sc.nextInt();
		int count = 0;
		if (x + y < d) {
			System.out.println(count);
			return;
		}
		int tx = 0;
		int ty = 0;
		if(x >= y){
			tx = d;
			while(tx >= 0 && ty <= y){
				tx-=1;
				ty+=1;
				count+=1;
			}
		}else{
			ty = d;
			while(ty >= 0 && tx <= x){
				ty-=1;
				tx+=1;
				count+=1;
		}
	}
		System.out.println(count);
	}
}