#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

char*mmap();
#define rd(v) int v=0;{int _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}
#define wt(v) {long _z=v;do*--wp=_z%10+48;while(_z/=10);}
#define rep(v,e) for(int v=0;v<e;++v)

void radix_sort_aux(unsigned*a,unsigned*b,int n){
	int c[512];
	for(int i=0;i<512;++i){
		c[i]=0;
	}
	for(int i=0;i<n;++i){
		++c[a[i]&511];
	}
	int t=0;
	for(int i=0;i<512;++i){
		int u=c[i];
		c[i]=t;
		t+=u;
	}
	for(int i=0;i<n;++i){
		b[c[a[i]&511]++]=a[i];
	}
}

void radix_sort(unsigned*a,int n){
	unsigned*b=a+n;
	radix_sort_aux(a,b,n);
	for(int i=0;i<n;++i){
		b[i]=b[i]>>8|b[i]<<24;
	}
	radix_sort_aux(b,a,n);
	for(int i=0;i<n;++i){
		a[i]=a[i]>>24|a[i]<<8;
	}
}

int a[400000];

main(){
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd(n);
	n<<=1;
	rep(i,n){
		rd(ai);
		a[i]=ai;
	}
	radix_sort(a,n);
	long r=0;
	for(int i=0;i<n;i+=2){
		r+=(long)a[i]*(long)a[i+1];
	}
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	wt(r);
	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}