Buggy python submission (verdict: Runtime Error):
from collections import deque
from heapq import heapify,heappop,heappush,heappushpop
from copy import copy,deepcopy
from itertools import product,permutations,combinations,combinations_with_replacement
from collections import defaultdict,Counter
from bisect import bisect_left,bisect_right
# from math import gcd,ceil,floor,factorial
# from fractions import gcd
from functools import reduce
from pprint import pprint

INF = float("inf")

def myinput():
    return map(int,input().split())

def mylistinput(n):
    return [ list(myinput()) for _ in range(n) ]

def mycol(data,col):
    return [ row[col] for row in data ]

def mysort(data,col,reverse_flag):
    data.sort(key=lambda x:x[col],reverse=reverse_flag)
    return data

def mymax(data):
    M = -1*float("inf")
    for i in range(len(data)):
        m = max(data[i])
        M = max(M,m)
    return M

def mymin(data):
    m = float("inf")
    for i in range(len(data)):
        M = min(data[i])
        m = min(m,M)
    return m

def mycount(ls,x):
    # lsはソート済みであること
    l = bisect_left(ls,x)
    r = bisect_right(ls,x)
    return (r-l)

def myoutput(ls,space=True):
    if space:
        if len(ls)==0:
            print(" ")
        elif type(ls[0])==str:
            print(" ".join(ls))
        elif type(ls[0])==int:
            print(" ".join(map(str,ls)))
        else:
            print("Output Error")
    else:
        if len(ls)==0:
            print("")
        elif type(ls[0])==str:
            print("".join(ls))
        elif type(ls[0])==int:
            print("".join(map(str,ls)))
        else:
            print("Output Error")

n = int(input())

for i in range(20):
    if i==0:
        r = 0
        l = n-1
        q = 0
        print(q)
    else:
        q = (r+l)//2
        print(q)
    s = input()
    m = s[0]
    if m=="V":
        exit()
    else:
        if i==0:
            b = m
        else:
            if b==m:
                r = q
            else:
                if q%2==1:
                    print(q+1)
                    s = input()
                    m = s[0]
                    if m=="V":
                        exit()
                    else:
                        print("E")
                        exit()
                else:
                    b = m
                    l = q
print("End")

Fixed submission:
from collections import deque
from heapq import heapify,heappop,heappush,heappushpop
from copy import copy,deepcopy
from itertools import product,permutations,combinations,combinations_with_replacement
from collections import defaultdict,Counter
from bisect import bisect_left,bisect_right
# from math import gcd,ceil,floor,factorial
# from fractions import gcd
from functools import reduce
from pprint import pprint

INF = float("inf")

def myinput():
    return map(int,input().split())

def mylistinput(n):
    return [ list(myinput()) for _ in range(n) ]

def mycol(data,col):
    return [ row[col] for row in data ]

def mysort(data,col,reverse_flag):
    data.sort(key=lambda x:x[col],reverse=reverse_flag)
    return data

def mymax(data):
    M = -1*float("inf")
    for i in range(len(data)):
        m = max(data[i])
        M = max(M,m)
    return M

def mymin(data):
    m = float("inf")
    for i in range(len(data)):
        M = min(data[i])
        m = min(m,M)
    return m

def mycount(ls,x):
    # lsはソート済みであること
    l = bisect_left(ls,x)
    r = bisect_right(ls,x)
    return (r-l)

def myoutput(ls,space=True):
    if space:
        if len(ls)==0:
            print(" ")
        elif type(ls[0])==str:
            print(" ".join(ls))
        elif type(ls[0])==int:
            print(" ".join(map(str,ls)))
        else:
            print("Output Error")
    else:
        if len(ls)==0:
            print("")
        elif type(ls[0])==str:
            print("".join(ls))
        elif type(ls[0])==int:
            print("".join(map(str,ls)))
        else:
            print("Output Error")

n = int(input())

print(0)
s = input()
m = s[0]
if m=="V":
    exit()
else:
    b = m
print(n-1)
s = input()
m = s[0]
if m=="V":
    exit()

for i in range(20):
    if i==0:
        r = 0
        l = n - 1
        q = (r+l)//2
    else:
        q = (r+l)//2
    print(q)
    s = input()
    m = s[0]
    if m=="V":
        exit()
    else:
        if m==b and (q-r+1)%2==1:
            r = q
        elif m==b and (q-r+1)%2==0:
            l = q
        elif m!=b and (q-r+1)%2==1:
            l = q
        elif m!=b and (q-r+1)%2==0:
            r = q
            b = m
        else:
            print("E")
print("End")