CodeForces 302C（数学）

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define INF 0x3f3f3f3f

using namespace std;

int n, m, sum, maxx, num, a[205];

int main()
{
while(~scanf("%d", &n))
{
m = 2*n - 1, sum = 0, num = 0;
for(int i=0;i<m;i++)
{
scanf("%d", &a[i]);
if(a[i] < 0)
{
a[i] = -a[i];
num++;
}
sum += a[i];
}

sort(a, a+m);
if(num%2==1 && n%2==0)
sum -= 2*a[0];

printf("%d\n", sum);
}

return 0;
}