I started off using the built-in bin() function, but it felt like the point was to do it myself, so I made user_bin to replicate it.

#!/bin/python3

import math
import os
import random
import re
import sys

def user_bin(n):
    n = int(n)
    out = ""
    while(n > 0):
        remainder = n % 2
        n = n//2
        out += str(remainder)
    return out[::-1]

if __name__ == '__main__':
    n = int(input().strip())
    print(max([len(i) for i in user_bin(n).split("0")]))

python 3

def base2(n):

mybin = bin(n)[2::]

return max(map(len, mybin.split('0')))

Pyhton

n = int(input())

binary_representation = bin(n)[2:]

consecutive_ones = binary_representation.split('0')

max_consecutive_ones = max(len(group) for group in consecutive_ones)

print(max_consecutive_ones)

My C# solution

public static void Main(string[] args) { int n = Convert.ToInt32(Console.ReadLine().Trim());

    string binary = Convert.ToString(n ,2);

    char[] c = binary.ToCharArray();

    int iCount = 1;   
    int left = 0;
    int right = 1;
    // This list will be used to store each count.
    // After each iteration, we add the count to the list.
    // After the loop has finished, we sort the elements in the 
    //list,
    // and finally, we print the last element of the list.
   List<int> lstCounts = new List<int>();

    for(int i = 0 ; i < c.Length ; i++)
    {
         if(right <= c.Length -1 )
        {
             if(c[left] == c[right] && c[right] == '1')
            { 
                iCount++;
                lstCounts.Add(iCount);
            }
             else 
             { 
                lstCounts.Add(iCount);
                iCount = 1;
             }
        }

        left++;
        right++;          
    }

// sort elements from the list  
 lstCounts.Sort();
 //print the highest count from the list
 Console.Write(lstCounts.LastOrDefault()); 


}