```go
package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var n int
	fmt.Fscan(in, &n)

	l := make([]int, n)
	r := make([]int, n)

	minL := int(1e9) + 1
	maxR := 0

	for i := 0; i < n; i++ {
		fmt.Fscan(in, &l[i], &r[i])
		if l[i] < minL {
			minL = l[i]
		}
		if r[i] > maxR {
			maxR = r[i]
		}
	}

	ans := -1
	for i := 0; i < n; i++ {
		if l[i] == minL && r[i] == maxR {
			ans = i + 1
			break
		}
	}

	fmt.Fprintln(out, ans)
}
```