// ErlangB Calculator C
// Author: Derek J Corbett
// Web: http://www.cs.usyd.edu.au/~dcorbett

#include <stdlib.h>
#include <stdio.h>
double erlang(int n, double a){
	double e;
	int i;
	e = 1.0;
 	for(i=1; i<=n; i++)
   	   e = 1.0 + e * i / a;
  	return (1.0 / e);
}

double find_erlang(int n, double p, double inc){
	double a;
	double cp;
	for(a = 0.00; ; a = a + inc){
		cp = erlang(n,a);
		if(cp > p){
			a = a - inc;
			break;
		}
	}
	return a;
}



int main(int argc, char** argv){
	float res;
	double inc;
 	if(argc < 3){
 		printf("Usage erlang N (channels) P (probability) I (increment)\n");
 		exit(1);
 	}
	if(argc == 3){
		inc = 0.01;
	}
	else{
		inc = (double)atof(argv[3]);
	}
	if((double)atof(argv[2]) >= 1 || (double)atof(argv[2]) <= 0){
		printf("Usage erlang N (channels) P (probability) I (increment)\nP must be between 1 and 0");
                exit(1);
	}
 	res = find_erlang(atoi(argv[1]),(double)atof(argv[2]),inc);
 	printf("%0.5f \n",res);
}