#include using namespace std; typedef int32_t h_int32; typedef int64_t h_int64; typedef uint32_t uh_int32; typedef uint64_t uh_int64; typedef h_int64 h_int; #define REP( i, n ) for(int i = 0; i < ( int )( n ); ++i ) #define REPR( i, n ) for(int i = ( int )( n ); i >= 0; --i) #define FOR( i, a, n ) for(int i = ( int )( a ); i < ( int )( n ); ++i ) #define FORR( i, a, n ) for(int i = ( int )( n ); i >= ( int )( a ); --i) #define VINIT( v, type, n )vector v; v.resize( n ); #define VINIT2( v, type, n, a )vector v; v.resize( n, a ); #define VCIN( v, type, n ) VINIT( v, type, n ) REP( i, n ) cin >> v[i]; #define ALL( x ) x.begin(), x.end() #define DOUT( x ) cerr << #x << " = " << x << "\n"; #define COUT( x ) cout << ( x ) << "\n"; #define INF 999999999 signed main() { ios::sync_with_stdio( false ); cin.tie( 0 ); int a, b, x, y; cin >> a >> b; cin >> x >> y; int dx = abs( a - x ); int dy = abs( b - y ); COUT( ( double )( dx + dy ) / 2.0 ); return 0; }