Make solution for 401 faster

python/e401.py

@@ -30,32 +30,13 @@ def sum2(a: int, b: int) -> int:
     return r
 
 
-def binsearch(a: int, d: int, n: int) -> int:
-    # Return the largest integer i in [a, n] for which n // i == d.
-
-    # Naive:
-    # b = a
-    # while n // (b + 1) == d:
-    #     b += 1
-    # return b
-
-    b = n
-    while n // b != d:
-        mid = (a + b) // 2
-        if b // mid != d:
-            b = mid
-        else:
-            a = mid
-    return b
-
-
 def sigma2caps(n: int) -> int:
     res = 0
     mod = 10**9
     a = 1
     while a <= n:
         d = n // a
-        b = binsearch(a, d, n)
+        b = n // d
         s2 = sum2(a, b) % mod
         res += (s2 * d) % mod
         res %= mod