Problem:
Score : 200 points

Problem Statement

Snuke is having a barbeque party.

At the party, he will make N servings of Skewer Meal.

Example of a serving of Skewer Meal

He has a stock of 2N skewers, all of which will be used in Skewer Meal. The length of the i-th skewer is L_i.
Also, he has an infinite supply of ingredients.

To make a serving of Skewer Meal, he picks 2 skewers and threads ingredients onto those skewers.
Let the length of the shorter skewer be x, then the serving can hold the maximum of x ingredients.

What is the maximum total number of ingredients that his N servings of Skewer Meal can hold, if he uses the skewers optimally?

Constraints

1≦N≦100

1≦L_i≦100

For each i, L_i is an integer.

Input

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

N
L_1 L_2 ... L_{2N}

Output

Print the maximum total number of ingredients that Snuke's N servings of Skewer Meal can hold.

Sample Input 1

2
1 3 1 2

Sample Output 1

3

If he makes a serving using the first and third skewers, and another using the second and fourth skewers, each serving will hold 1 and 2 ingredients, for the total of 3.

Sample Input 2

5
100 1 2 3 14 15 58 58 58 29

Sample Output 2

135

Solution in C (GCC 5.4.1) (judge verdict: Runtime Error)

typedef long unsigned int size_t;
extern int printf (const char *__restrict __format, ...);
extern int scanf (const char *__restrict __format, ...) ;
extern int getchar (void);
extern int putchar (int __c);
int nextInt(){int f=0;char s=0;char c=getchar();while((c<48)||(57<c)){if(c==45){s=1;c=getchar();break;}c=getchar();}while((48<=c)&&(c<=57)){f=f*10+(c-48);c=getchar();}return s?-f:f;}
char nextChar(){char f=0;char s=0;char c=getchar();while((c<48)||(57<c)){if(c==45){s=1;c=getchar();break;}c=getchar();}while((48<=c)&&(c<=57)){f=f*10+(c-48);c=getchar();}return s?-f:f;}
short int nextShort(){short f=0;char s=0;char c=getchar();while((c<48)||(57<c)){if(c==45){s=1;c=getchar();break;}c=getchar();}while((48<=c)&&(c<=57)){f=f*10+(c-48);c=getchar();}return s?-f:f;}
long long int nextLong(){long long int f=0;char s=0;char c=getchar();while((c<48)||(57<c)){if(c==45){s=1;c=getchar();break;}c=getchar();}while((48<=c)&&(c<=57)){f=f*10+(c-48);c=getchar();}return s?-f:f;}
void println(){putchar(10);}
void print(char *f){while(*f){putchar(*f);f++;}}
void printInt(int f){char c[10];if(!f){putchar(48);return;}if(f<0){f=-f;putchar(45);}char i=0;while(f){c[++i]=(f%10)+48;f/=10;}while(i){putchar(c[i--]);}}
void printLong(long long int f){char c[19];if(!f){putchar(48);return;}if(f<0){f=-f;putchar(45);}char i=0;while(f){c[++i]=(f%10)+48;f/=10;}while(i){putchar(c[i--]);}}
typedef int (*__compar_fn_t) (const void *, const void *);
extern void *bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size, __compar_fn_t __compar)__attribute__ ((__nonnull__ (1, 2, 5))) ;
extern void qsort (void *__base, size_t __nmemb, size_t __size, __compar_fn_t __compar) __attribute__ ((__nonnull__ (1, 4)));
int compare_int(const void *a, const void *b){return *(int*)a - *(int*)b;}
int compare_char(const void *a, const void *b){return *(char*)a - *(char*)b;}
int compare_short(const void *a, const void *b){return *(short*)a - *(short*)b;}
int compare_long(const void *a, const void *b){if(*(long long int*)a - *(long long int*)b < 0){return -1;}else if(*(long long int*)a - *(long long int*)b > 0){return 1;}else{return 0;}}
char n, i;
char l[200];
int ans;
int main(){
 n = nextChar()*2;
 for(i=0; i<n; i++){
  l[i] = nextChar();
 }
 qsort(l, n, sizeof(char), compare_char);
 for(i=0; i<n; i+=2){
  ans += l[i];
 }
 printInt(ans);
 println();
}