#include <stdio.h>

int max(int x, int y){
	if(x>y){	return x;	}
	return y;
}

int min(int x, int y){
	if(x<y){	return x;	}
	return y;
}

int main(void){
	int x,y,d;
	int ans;
	scanf("%d %d %d", &x, &y, &d);
	
	if( max(x,y) <= d ){
		ans = 2*max(x,y)-d-(max(x,y)-min(x,y))+1;
	}else if(min(x,y) >= d){
		ans = d+1;
	}else{
		ans = 2*max(min(x,y),d)-d-(max(min(x,y),d)-min(min(x,y),d))+1;
	}
	
	if(ans < 0){ans=0;}
	printf("%d\n", ans);
	
	return 0;
}