FOJ_1001_Duplicate Pair

  

An array of length n, with address from 1 to n inclusive, contains entries from the set {1,2,...,n-1} and there's exactly two elements with the same value. Your task is to find out the value.

Input

Input contains several cases.
Each case includes a number n (1<n<=10^6), which is followed by n integers.
The input is ended up with the end of file.

Output

Your must output the value for each case, one per line.

Sample Input

21 141 2 3 2

Sample Output

12

#include<stdio.h>

int main()

{

long long int sum,num;

long int n,a,cfs,i;

while(scanf("%ld",&n)!=EOF)

{

num=0;

sum=0;

for(i=1;i<n;i++)

sum+=i;

for(i=0;i<n;i++)

{

scanf("%ld",&a);

num+=a;

}

cfs=num-sum;

printf("%ld/n",cfs);

}

return 0;

}

 我是直接暴力算-___________________-