arr = []

n = int(input("enter size of array : "))

for x in range(n-1):

x=int(input("enter element of array : "))

arr.append(x)

sum = (n*(n+1))/2;

sumArr = 0

for i in range(n-1):

sumArr = sumArr+arr[i];

print(int(sum-sumArr))

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