JSFiddle - React, Tailwind, and code Playground

JavaScript

var A = [2, 1, 3, 4, 5];
var B = [];
var n = 5
var m = 12
big = -1;
for (i = 0; i < n; i++) {
    sum=0;
    for (j = i; j < n; j++) {
        sum += A[j];
        if (sum <= m) { B[i] = sum; continue; }
        if (sum > m) { B[i] = (sum - A[j]); break; }
        if (sum == m) {
            break;
        }
    }
    if (B[i] > big)
        big = B[i];
}
alert(big);