#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;}

int h[200000];

main(){
	char*rp=mmap(0l,800l<<10,1,2,0,0ll);
	while(*rp++!=32);
	RD(x);
	long z=0;
	if(x<=200000){
		do{
			RD(a);
			z+=x-a>=0?h[x-a]:0;
			++h[a];
		}while(*rp);
		z+=z;
		z+=x&1?0:h[x>>1];
	}
	char wbuf[16],*wp=wbuf+sizeof wbuf;
	while(*--wp=z%10+48,z/=10);
	write(1,wp,(wbuf+sizeof wbuf)-wp);
	_exit(0);
}