```go
package main

import (
	"fmt"
)

func main() {
	var a, b, c, d int
	fmt.Scan(&a, &b, &c, &d)

	var ans int64
	// We iterate over the sum of x and y, let s = x + y.
	// The range of s is [A+B, B+C].
	// For a non-degenerate triangle, we need x + y > z => s > z => z < s.
	// Also C <= z <= D. So we need z in [C, min(D, s-1)].
	// If min(D, s-1) < C, there are no valid z. Thus s-1 >= C => s >= C+1.
	
	start := a + b
	if c+1 > start {
		start = c + 1
	}

	for s := start; s <= b+c; s++ {
		// Calculate number of pairs (x, y) such that x+y = s
		// Constraints: A <= x <= B, B <= y <= C
		// x = s - y
		// B <= y <= C => B <= s - x <= C => s - C <= x <= s - B
		// Combined with A <= x <= B:
		// x in [max(A, s-C), min(B, s-B)]
		
		l := a
		if s-c > l {
			l = s - c
		}
		r := b
		if s-b < r {
			r = s - b
		}

		if l > r {
			continue
		}
		
		countXY := int64(r - l + 1)

		// Calculate number of z
		zMax := d
		if s-1 < zMax {
			zMax = s - 1
		}
		
		// Since s >= c + 1, zMax >= c is guaranteed.
		countZ := int64(zMax - c + 1)

		ans += countXY * countZ
	}

	fmt.Println(ans)
}
```