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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