#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 wt(v) if(v>=100000000){WTHI(v/10);*wp++=v%10+'0';}else{WTHI(v);}
#define repeat(e) for(typeof(e)_=e;_--;)

char wbuf[1<<25];

int main(){
	char*wp=wbuf;
	rd_init();
	int t=rd();
	repeat(t){
		int n=rd();
		int k=rd();
		redo:;
		if(n==k){
			*wp++='-';
			*wp++='1';
		}else{
			for(int i=(n-1)/k+1;i*i<=n;++i){
				if(n%i==0){
					--n;
					goto redo;
				}
			}
			wt(n);
		}
		*wp++='\n';
	}
	write(1,wbuf,wp-wbuf);
	_exit(0);
}