#include<iostream>#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>using namespace std;const int MAX=10000;int pri[MAX+5];int mark[MAX+5];int cnt;int p1[MAX+5],p2[MAX+5],p3[MAX+5],p4[MAX+5],x1[MAX+5],x2[MAX+5];void Prime(){ int i,j; cnt=0; for(i=0;i<MAX;i++) mark[i]=i; for(i=2;i<MAX;i++) { if(mark[i]==i) pri[cnt++]=i; for(j=0;j<cnt&&pri[j]*i<MAX;j++) { mark[i*pri[j]]=pri[j]; if(i%pri[j]==0) break; } }}void solve(int x,int y,int p[]){ int i,j,n; for(i=x;i<=y;i++) { n=i; for(j=0;j<cnt;j++) { if(n%pri[j]==0) { while(n%pri[j]==0) { p[pri[j]]++; n=n/pri[j]; } } if(n==1) break; } }}int main(){ Prime(); int p,q,r,s,i,j; while(scanf("%d%d%d%d",&p,&q,&r,&s)!=EOF) { q=min(p-q,q); s=min(r-s,s); memset(p1,0,sizeof(p1)); memset(p2,0,sizeof(p2)); memset(p3,0,sizeof(p3)); memset(p4,0,sizeof(p4)); solve(p-q+1,p,p1); solve(1,s,p2); solve(1,q,p3); solve(r-s+1,r,p4); for(i=0;i<MAX;i++) { x1[i]=p1[i]+p2[i]; x2[i]=p3[i]+p4[i]; } double ans=1.0; for(i=0;i<MAX;i++) { if(x1[i]>x2[i]) { for(j=1;j<=x1[i]-x2[i];j++) ans=ans*i; } else { for(j=1;j<=x2[i]-x1[i];j++) { ans=ans/i; } } } printf("%.5lfn",ans); } return 0;}
