#include using namespace std; #define all(c) (c).begin(),(c).end() #define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--) #define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++) #define rep(i,n) REP(i,0,n) #define iter(c) __typeof((c).begin()) #define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++) #define mem(a) memset(a,0,sizeof(a)) #define pd(a) printf("%.10f\n",a) #define pb(a) push_back(a) #define in(a) insert(a) #define pi M_PI #define R cin>> #define F first #define S second #define C class #define ll long long #define ln cout<<'\n' templatevoid pr(T a){cout<void pr(T a,T2 b){cout<void pr(T a,T2 b,T3 c){cout<void PR(T a,int n){rep(i,n){if(i)cout<<' ';cout<=0&&x=0&&y P; void Main() { double x,y,s,t; cin >> x >> y >> s >> t; pd((abs(x-s)+abs(y-t))/2); } int main() { ios::sync_with_stdio(0);cin.tie(0); Main();return 0; }