#include<stdio.h>#include<math.h>#include<algorithm>#define MAXV 2000#define PI 3.14159265358979323846#define eps 1e-8#define zero( x ) ( fabs( x ) < eps )#define _sign( x ) ( ( x ) > eps ?1 : ( ( x ) < -eps ?2 : 0 ) )using namespace std;struct pt{ double x , y; pt() {} pt( double _x , double _y ) { x = _x; y = _y; } pt operator - ( const pt p1 ) { return pt( x - p1.x , y - p1.y ); } pt operator + ( const pt p1 ) { return pt( x + p1.x , y + p1.y ); } pt operator / ( double r ) { return pt( x / r , y / r ); } pt operator * ( double r ) { return pt( x * r , y * r ); } bool operator == ( const pt p1 ) const{ return fabs( x-p1.x ) < eps && fabs( y-p1.y ) < eps; } bool operator != ( const pt p1 ) const{ return fabs( x-p1.x ) > eps || fabs( y-p1.y ) > eps; } bool operator < ( const pt p1 ) const{ return y < p1.y-eps || y < p1.y+eps && x < p1.x; }};double cpr( const pt &a , const pt &b , const pt &c ) { return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x); }double dpr( const pt &a , const pt &b , const pt &c ) { return (b.x-a.x)*(c.x-a.x)+(b.y-a.y)*(c.y-a.y); }double cpr( const pt &a , const pt &b ) { return a.x*b.y-a.y*b.x; }double dpr( const pt &a , const pt &b ) { return a.x*b.x+a.y*b.y; }double dis( const pt &a , const pt &b ) { return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); }double disptoseg( pt p , pt a , pt b ){ pt t = p; t.x += a.y - b.y; t.y += b.x - a.x; if ( cpr( p , a , t )*cpr( p , b , t ) > eps ) return min( dis( p , a ) , dis( p , b ) ); return fabs( cpr( b , p , a ) ) / dis( a , b );}pt its( const pt &a , const pt &b , const pt &c , const pt &d ){ pt ret = a; double t = ( ( c.x - a.x )*( d.y - c.y ) - ( c.y - a.y )*( d.x - c.x ) ) / ( ( b.x - a.x )*( d.y - c.y ) - ( b.y - a.y )*( d.x - c.x ) ); ret.x += ( b.x - a.x )*t; ret.y += ( b.y - a.y )*t; return ret;}void half_its( pt &a , pt &b , pt pol[] , int &polcnt , pt exch[] ){ int i , p2 = 0; bool now , last = cpr( a , b , pol[ polcnt-1 ] ) > -eps; for ( int i = 0 ; i < polcnt ; i++ ) { now = cpr( a , b , pol[ i ] ) > -eps; if ( now ^ last ) exch[ p2++ ] = its( a , b , pol[ i ] , pol[ ( i+polcnt-1 ) % polcnt ] ); if ( now ) exch[ p2++ ] = pol[ i ]; last = now; } polcnt = p2; for ( i = 0 ; i < p2 ; i++ ) pol[ i ] = exch[ i ]; }constint maxn = 1007;double maxnum = 1000000000000ll;int n , tot , test;pt num[ maxn ] , pol[ maxn ] , exch[ maxn ];void work(){ scanf( "%d" , &n ); for ( int i = 1 ; i <= n ; i++ ) scanf( "%lf %lf" , &num[ i ].x , &num[ i ].y ); tot = 4; pol[ 0 ].x = -maxnum; pol[ 0 ].y = maxnum; pol[ 1 ].x = -maxnum; pol[ 1 ].y = -maxnum; pol[ 2 ].x = maxnum; pol[ 2 ].y = -maxnum; pol[ 3 ].x = maxnum; pol[ 3 ].y = maxnum; for ( int i = 1 ; i <= n-1 ; i++ ) half_its( num[ i ] , num[ i+1 ] , pol , tot , exch ); double ans = maxnum , tmp; pt tt;for ( int i = 1 ; i <= n ; i++ ) for ( int j = 0 ; j <= tot-2 ; j++ ) if ( num[ i ].x > pol[ j ].x && num[ i ].x < pol[ j+1 ].x ) { tt.x = num[ i ].x; tt.y = 0; tt = its( num[ i ] , tt , pol[ j ] , pol[ j+1 ] ); tmp = dis( num[ i ] , tt ); if ( tmp < ans ) ans = tmp; } for ( int i = 0 ; i <= tot-1 ; i++ ) for ( int j = 1 ; j <= n-1 ; j++ ) if ( pol[ i ].x > num[ j ].x && pol[ i ].x < num[ j+1 ].x ) { tt.x = pol[ i ].x; tt.y = 0; tt = its( pol[ i ] , tt , num[ j ] , num[ j+1 ] ); tmp = dis( pol[ i ] , tt ); if ( tmp < ans ) ans = tmp; }if ( ans > 1000+eps ){ printf( "IMPOSSIBLEn" ); return;} printf( "%.1lfn" , ans );}int main(){ scanf( "%d" , &test ); for ( int run = 1 ; run <= test ; run++ ) work();}
