#define NDEBUG

#undef __STRICT_ANSI__

#include <cstdlib>
#include <cstdio>
#include <tuple>
#include <vector>
#include <algorithm>
#include <functional>
#include <cstring>
#include <cmath>
#include <cfloat>
#include <cassert>

using namespace std;

#undef assert
#define assert(e)

#include <cstdarg>

const char * format(const char * fmt, ...) {
	static char buf[65536];
	va_list arg;
	va_start(arg, fmt);
	vsprintf(buf, fmt, arg);
	va_end(arg);
	return buf;
}

void info(const char * format, ...) {
	va_list arg;
	va_start(arg, format);
	vfprintf(stderr, format, arg);
	va_end(arg);
}

void gvUsing(function<void()> func) {
	func();
}

#include <sys/time.h>

class XsRandom {
	unsigned long long a;
	unsigned long long b;
public:
	inline XsRandom() : a(0x8a5cd789635d2dffULL), b(0x121fd2155c472f96ULL) {
	}
	inline XsRandom(const XsRandom & o) : a(o.a), b(o.b) {
	}
	inline unsigned long long next64() {
		unsigned long long c = a ^ (a<<23);
		a = b;
		b = c ^ a ^ (c>>18) ^ (a>>5);
		return b + a;
	}
	inline XsRandom(unsigned int seed) : a(0x8a5cd789635d2dffULL), b(0x121fd2155c472f96ULL) {
		seed = seed * 1234567891 + 521288629;
		unsigned long long a2 = a;
		unsigned long long b2 = b;
		while(seed) {
			next64();
			if(seed & 1) {
				a2 ^= a;
				b2 ^= b;
			}
			seed >>= 1;
		}
		a = a2;
		b = b2;
	}
	inline unsigned int next() {
		return (unsigned int)next64();
	}
	inline int nextInt(int r) {
		assert(1<=r);
		return ((unsigned long long)next() * r)>>32;
	}
};

typedef XsRandom MyRandom;

MyRandom g_myRand;

static inline double getTime2(){
	timeval tv;
	gettimeofday(&tv, 0);
	double result = tv.tv_sec + tv.tv_usec * 1e-6;
	return result;
}
static double g_startTime;
static double g_suspendTime = 0;
const double g_timeupSecBase = 9.8;
double g_timeupSec = g_timeupSecBase;

double watch(const char * format, function<void()> func, ...) {
	double start = getTime2();
	func();
	double spend = getTime2() - start;
	{
		va_list arg;
		va_start(arg, func);
		char buf[4096];
		int ret = vsnprintf(buf, sizeof(buf), format, arg);
		va_end(arg);
		if((int)sizeof(buf)<=ret) {
			buf[sizeof(buf)-1] = '\0';
		}
		info("%s: %fsec\n", buf, spend);
	}

	return spend;
}

double watch(function<void()> func) {
	return watch("time", func);
}

#include <numeric>

template<bool bigIsBetter>double searchConvex(function<double(double)> func, double a, double d, int n=20) {
	double b = (d-a)*0.381966+a;
	double c = (a-d)*0.381966+d;
	double bV = func(b);
	double cV = func(c);
	for(int i=0; i<n; ++i) {
		if(bigIsBetter ? cV<bV : bV<cV) {
			d = c;
			c = b;
			b = (d-a)*0.381966+a;
			cV = bV;
			bV = func(b);
		}
		else {
			a = b;
			b = c;
			c = (a-d)*0.381966+d;
			bV = cV;
			cV = func(c);
		}
	}
	if(bigIsBetter ? cV<bV : bV<cV) {
		return b;
	}
	else {
		return c;
	}
}

const char * nextCLineOrWord(int mode) {
	static char buf[65536];
	static int bufLen = sizeof(buf);
	static int bufPos = sizeof(buf);
	static bool canReadFlag = true;
	static bool crFlag = false;
	static bool enterFlag = false;
	if(canReadFlag && (enterFlag ? bufLen<=bufPos : (int)sizeof(buf)<=bufPos+bufPos)) {
		if(0<bufLen-bufPos) {
			memmove(buf, buf+bufPos, bufLen-bufPos);
			bufLen -= bufPos;
		}
		else {
			bufLen = 0;
		}
		char * result = fgets(buf+bufLen, sizeof(buf)-bufLen, stdin);
		canReadFlag = (result!=NULL);
		if(result!=NULL) {
			int n = strlen(result);
			enterFlag = (n!=(int)sizeof(buf)-1-bufLen || (1<=bufLen+n && buf[bufLen+n-1]=='\n'));
			bufLen += n;
		}
		bufPos = 0;
	}
	if(mode==0) {
		int pos = bufPos;
		while(true) {
			char c = buf[pos];
			if(c==32) {
				buf[pos++] = '\0';
				break;
			}
			else if(c==10) {
				if(crFlag) {
					crFlag = false;
					if(bufPos==pos) {
						pos = ++bufPos;
						continue;
					}
				}
				buf[pos++] = '\0';
				break;
			}
			else if(c==13) {
				crFlag = true;
				buf[pos++] = '\0';
				break;
			}
			else if(c==0) {
				break;
			}
			++pos;
		}
		const char * ret = buf + bufPos;
		bufPos = pos;
		return ret;
	}
	else if(mode==1) {
		int pos = bufPos;
		while(true) {
			char c = buf[pos];
			if(c==10) {
				if(crFlag) {
					crFlag = false;
					if(bufPos==pos) {
						pos = ++bufPos;
						continue;
					}
				}
				buf[pos++] = '\0';
				break;
			}
			else if(c==13) {
				crFlag = true;
				buf[pos++] = '\0';
				break;
			}
			else if(c==0) {
				break;
			}
			++pos;
		}
		const char * ret = buf + bufPos;
		bufPos = pos;
		return ret;
	}
	else if(mode==2) {
		return bufLen<=bufPos ? NULL : buf+bufPos;
	}
	assert(false);
	return NULL;
}

const char * nextCWord() {
	return nextCLineOrWord(0);
}

int nextInt() {
	return atoi(nextCWord());
}

vector<int> nextIntVec(int n) {
	vector<int> ret;
	for(int i=0; i<n; ++i) {
		ret.push_back(nextInt());
	}
	return ret;
}

void echoln() {
	fputc('\n', stdout);
}
void echoln(const char * format, ...) {
	va_list arg;
	va_start(arg, format);
	vprintf(format, arg);
	va_end(arg);
	fputc('\n', stdout);
}

int main() {
	int N = nextInt();
	auto L = nextIntVec(2*N);
	sort(L.begin(), L.end());
	int ret = 0;
	for(int i=0; i<N; ++i) {
		ret += L[i*2];
	}
	echoln("%d", ret);

	return 0;
}


Measured memory_bytes: 256