#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define REP(i,n) for(int (i)=0;(i)<(n);(i)++) #define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++) #define RREP(i,a) for(int (i)=(a)-1;(i)>=0;(i)--) #define FORR(i,a,b) for(int (i)=(a)-1;(i)>=(b);(i)--) #define PI acos(-1.0) #define DEBUG(C) cout< #define VII vector #define VL vector #define VLL vector #define VD vector #define VDD vector #define PII pair #define PDD pair #define PLL pair #define VPII vector #define ALL(a) (a).begin(),(a).end() #define SORT(a) sort(ALL(a)) #define REVERSE(a) reverse(ALL(a)) #define MP make_pair #define FORE(a,b) for(auto &&a:b) using namespace std; typedef long long LL; typedef unsigned long long ULL; const int INF=1e9; const int MOD=INF+7; int main (void){ int px,py,qx,qy; cin>>px>>py>>qx>>qy; int dis=abs(qy-py)+abs(qx-px); cout<<(double)(dis/2.0)<