15 lines
256 B
Python
15 lines
256 B
Python
import sys
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input=sys.stdin.readline
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n=int(input().rstrip())
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arr=list(map(int,input().rstrip().split()))
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last=0
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result=0
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for i in range(1,n+1):
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if arr[-i]>last:
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last+=1
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elif arr[-i]<last:
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last=arr[-i]
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result+=last
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print(result)
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