let arr = [1,2,5,4,6,3]
function maxNum (arr, n) {
let max = 0
for (let i = 0; i<arr.length;i++){
let curNum = 0
for (let j=i;j<(n+i);j++){
curNum += arr[j]
}
if (curNum > max) {
max = curNum
}
}
return max
}
console.log(maxNum(arr,2))