Problem:
Score : 100 points

Problem Statement

Joisino wants to evaluate the formula "A op B".
Here, A and B are integers, and the binary operator op is either + or -.
Your task is to evaluate the formula instead of her.

Constraints

1≦A,B≦10^9

op is either + or -.

Input

The input is given from Standard Input in the following format:

A op B

Output

Evaluate the formula and print the result.

Sample Input 1

1 + 2

Sample Output 1

3

Since 1 + 2 = 3, the output should be 3.

Sample Input 2

5 - 7

Sample Output 2

-2

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
long long int po(long long int x){
    if(x==0)return 1;
    if(x%2==0) return (po(x/2)%1000000007)*(po(x/2)%1000000007);
    else return 2*(po(x-1)%1000000007);
}

int main(){
    int n;
    scanf("%d",&n);
    int a,i;
    int count[n];
    for(i=0;i<=n-1;i++)count[i]=0;
    for(i=0;i<=n-1;i++){
        scanf("%d",&a);
        count[a]+=1;
    }
    int flag=0;
    if(n%2==0) {
        for(i=0;i<=n/2-1;i++){
            if(count[2*i+1]!=2)flag=1;
        }
    }else{
        if(count[0]!=1)flag=1;
        for(i=1;i<=n/2;i++){
            if(count[2*i]!=2)flag=1;
        }
    }
    if(flag==1)printf("0");
    else printf("%lld",po(n/2));
    return 0;
}