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#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <set>
#include <vector>
using namespace std;
const int INF = ~0u>>1;
typedef pair <int,int> P;
#define MID(x,y) ((x+y)>>1)
#define iabs(x) ((x)>0?(x):-(x))
#define REP(i,a,b) for(int i=(a);i<(b);i++)
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define pb push_back
#define mp make_pair
#define print() cout<<"--------"<<endl
#define EPS 1e-10
bool check(int a,int b,int c){
if (a && b && c && a + b > c && a + c > b && b + c > a)
return 1;
else return 0;
}
double solve(int a,int b,int c){
double p = (a+b+c+0.0)/2;
return sqrt(p * (p-a) * (p-b) * (p-c));
}
double ans = 0.0;
int a,b,c,cnt;
bool vis[12];
int num[4][3];
void dfs(int i){
if (i > 3){
if (check(a,b,c))
ans = max(ans,solve(a,b,c));
return;
}
for (int j = 0; j < 6; j ++){
if (j < 3){
switch(j){
case 0:a += num[i][1] + num[i][2]; dfs(i+1); a-=(num[i][1] + num[i][2]); break;
case 1:b += num[i][1] + num[i][2]; dfs(i+1); b-=(num[i][1] + num[i][2]);break;
case 2:c += num[i][1] + num[i][2]; dfs(i+1); c-=(num[i][1] + num[i][2]);break;
}
}
if (!vis[j]){
if (j == 3){
vis[j] = 1;
a += num[i][1];
c += num[i][2];
dfs(i+1);
a -= num[i][1];
c -= num[i][2];
vis[j] = 0;
vis[j] = 1;
a += num[i][2];
c += num[i][1];
dfs(i+1);
a -= num[i][2];
c -= num[i][1];
vis[j] = 0;
}
else if (j == 4){
vis[j] = 1;
a += num[i][1];
b += num[i][2];
dfs(i+1);
a -= num[i][1];
b -= num[i][2];
vis[j] = 0;
vis[j] = 1;
a += num[i][2];
b += num[i][1];
dfs(i+1);
a -= num[i][2];
b -= num[i][1];
vis[j] = 0;
}
else if (j == 5){
vis[j] = 1;
b += num[i][1];
c += num[i][2];
dfs(i+1);
b -= num[i][1];
c -= num[i][2];
vis[j] = 0;
vis[j] = 1;
b += num[i][2];
c += num[i][1];
dfs(i+1);
b -= num[i][2];
c -= num[i][1];
vis[j] = 0;
}
}
}
}
int main(){
while (~scanf("%d%d",&num[1][1], &num[1][2])){
scanf("%d%d",&num[2][1], &num[2][2]);
scanf("%d%d",&num[3][1], &num[3][2]);
ans = 0.0;a=b=c=0;
memset(vis,0,sizeof(vis));
dfs(1);
printf("%.9fn",ans);
}
return 0;
}
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