1000.js

var N = 1000,
    digits = "",
    sums = [],
    i,l,n,sum,sub;

for (n = 1; n <= N; ++n) {
  digits += Math.floor(Math.random() * 10);
}

for (n = 0; n <= (N-6); ++n) {
  sub = digits.substr(n, 5);
  sum = 0;
  for (i = 0, l = sub.length; i < l; i++) {
    sum += +sub[i];
  }
  sums.push([(sum<10?"0"+sum:sum), n, sub].join(":"));
}

print(sums.sort().pop());