788 B | 788 chars
import sys
from math import sqrt, pi, sin, factorial
BLANK = " "
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def f(s):
t, team = s.split()
m, s, ss = map(int, t.split(":"))
tm = ss + s * 1000 + m * 60000
return (tm, team)
def solve():
while 1:
try:
n = ii()
l = mii()
except:
break
if n == 1:
print(1)
continue
diff = l[-1] - l[-2]
idx = n - 2
while idx > -1:
if l[idx + 1] - l[idx] == diff:
idx -= 1
else:
break
print(idx + 2)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()