Sky Online Judge

#	State	Memory
0	Memory Limit ExceedMLE	1052672
1	Memory Limit ExceedMLE	1052672
2	Memory Limit ExceedMLE	1052672
3	Memory Limit ExceedMLE	1052672

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n = int(input())
sum = 0
for i in range(n):
    sum += i
    
print(sum)
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX