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

#define rd_init() char*rp=({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({int _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define WTHI(v) {unsigned _z=v,_n=0;long _d=0;while(++_n,_d=_d<<8|0x30|_z%10,_z/=10);*(long*)wp=_d;wp+=_n;}
#define WTLO(v) {unsigned _z=v,_n=8;long _d=0;while(_d=_d<<8|0x30|_z%10,_z/=10,--_n);*(long*)wp=_d;wp+=8;}
#define wt(v) if(v>=100000000){WTHI(v/100000000);WTLO(v%100000000);}else{WTHI(v);}
#define rep(v,e) for(typeof(e)v=0;v<e;++v)

typedef unsigned long ulong;

void sort_aux(ulong*a,ulong*b,int n){
	int c[256];
	for(int i=0;i<256;++i){
		c[i]=0;
	}
	for(int i=0;i<n;++i){
		++c[a[i]&255];
	}
	int t=0;
	for(int i=0;i<256;++i){
		int u=c[i];
		c[i]=t;
		t+=u;
	}
	for(int i=0;i<n;++i){
		b[c[a[i]&255]++]=a[i]>>8|a[i]<<56;
	}
}

void sort(ulong*a,int n){
	static ulong b[400000];
	sort_aux(a,b,n);
	sort_aux(b,a,n);
	sort_aux(a,b,n);
	sort_aux(b,a,n);
}

char wbuf[1<<25];
ulong a[400000];
int n;

f1(){
	rd_init();
	n=rd();
	rep(i,n*2){
		a[i]=(ulong)(i+1)<<32|rd();
	}
}

f2(){
	char*wp=wbuf;		
	ulong z=0;
	rep(i,n){
		z+=(a[i+n]>>32)-(a[i]>>32);
	}
	wt(z);
	*wp++='\n';
	rep(i,n){
		WTHI(a[i]);
		*wp++=' ';
		WTHI(a[i+n]);
		*wp++='\n';
	}
	write(1,wbuf,wp-wbuf);
}

int main(){
	f1();
	sort(a,n*2);
	f2();
	_exit(0);
}