Problem p02801 (python)

Fixed submission:
c=str(input())
if c == 'a' :
    print("b")
elif c == 'b' :
    print("c")
elif c == 'c' :
    print("d")
elif c == 'd' :
    print("e")
elif c == 'e' :
    print ("f")
elif c == 'f' :
    print("g")
elif c == 'g' :
    print("h")
elif c == 'h' :
    print("i")
elif c == 'i' :
    print("j")
elif c == 'j' :
    print("k")
elif c == 'k' :
    print("l")
elif c == 'l' :
    print("m")
elif c == 'm' :
    print("n")
elif c == 'n' :
    print("o")
elif c == 'o' :
    print("p")
elif c == 'p' :
    print("q")
elif c == 'q' :
    print("r")
elif c == 'r' :
    print("s")
elif c == 's' :
    print("t")
elif c == 't' :
    print("u")
elif c == 'u' :
    print("v")
elif c == 'v' :
    print("w")
elif c == 'w' :
    print("x")
elif c == 'x' :
    print("y")
elif c == 'y' :
    print("z")

Buggy submission (verdict: Runtime Error):
c = input()
abc = 'abcdefghijklmnopqrstuvwxyz'
for i in range(26) :
    if abc[i] == c
        print(abc[i+1])
        break

Buggy submission (verdict: Runtime Error):
c=int(input())
if c == a :
    print("b")
elif c == b :
    print("c")
elif c == c :
    print("d")
elif c == d :
    print("e")
elif c == e :
    print ("f")
elif c == f :
    print("g")
elif c == g :
    print("h")
elif c == h :
    print("i")
elif c == i :
    print("j")
elif c == j :
    print("k")
elif c == k :
    print("l")
elif c == l :
    print("m")
elif c == m :
    print("n")
elif c == n :
    print("o")
elif c == o :
    print("p")
elif c == p :
    print("q")
elif c == q :
    print("r")
elif c== r :
    print("s")
elif c == s :
    print("t")
elif c == t :
    print("u")
elif c == u :
    print("v")
elif c == v :
    print("w")
elif c == w :
    print("x")
elif c == x :
    print("y")
elif c == y :
    print("z")

Buggy submission (verdict: Runtime Error):
c=str(input())
print(c+1)

Buggy submission (verdict: Runtime Error):
c=str()
print(c+1)

Buggy submission (verdict: Runtime Error):
c=int(input())
print(c+1)

Buggy submission (verdict: Runtime Error):
c=input()
print(c+1)

Buggy submission (verdict: Runtime Error):
c=input()
if c == a :
    print("b")
elif c == b :
    print("c")
elif c == c :
    print("d")
elif c == d :
    print("e")
elif c == e :
    print ("f")
elif c == f :
    print("g")
elif c == g :
    print("h")
elif c == h :
    print("i")
elif c == i :
    print("j")
elif c == j :
    print("k")
elif c == k :
    print("l")
elif c == l :
    print("m")
elif c == m :
    print("n")
elif c == n :
    print("o")
elif c == o :
    print("p")
elif c == p :
    print("q")
elif c == q :
    print("r")
elif c== r :
    print("s")
elif c == s :
    print("t")
elif c == t :
    print("u")
elif c == u :
    print("v")
elif c == v :
    print("w")
elif c == w :
    print("x")
elif c == x :
    print("y")
elif c == y :
    print("z")

Buggy submission (verdict: Runtime Error):
c=int(input())
if c == a :
    print("b")
elif c == b :
    print("c")
elif c == c :
    print("d")
elif c == d :
    print("e")
elif c == e :
    print ("f")
elif c == f :
    print("g")
elif c == g :
    print("h")
elif c == h :
    print("i")
elif c == i :
    print("j")
elif c == j :
    print("k")
elif c == k :
    print("l")
elif c == l :
    print("m")
elif c == m :
    print("n")
elif c == n :
    print("o")
elif c == o :
    print("p")
elif c == p :
    print("q")
elif c == q :
    print("r")
elif c== r :
    print("s")
elif c == s :
    print("t")
elif c == t :
    print("u")
elif c == u :
    print("v")
elif c == v :
    print("w")
elif c == w :
    print("x")
elif c == x :
    print("y")
elif c == y :
    print("z")