POJ-2006

#include<iostream>#include<cmath>#include<cstdio>using namespace std;int main(int argc, char *argv[]){double k,a;int m,n;while(cin>>k>>a>>m>>n,k||a||m||n){double hC=(-1*k+sqrt(k*k+4*a*k*m*n))/2/n;double pH=-1*log10(hC);printf("%0.3f\n",pH);}return 0;}