#include<iostream.h>
#include<math.h>
double f(double x)
{
 if(x==0)
  return 1;
 else
 return sin(x)/x;
}
double ff(double a,double b,double c)
{
 double h=b-a;
 double t1,t2=0,x,s=0;
 t1=(h/2)*(f(a)+f(b));
 while(fabs(t2-t1)>c)
 {
  s=0;x=a+h/2;
  t1=t2;
  while(x<b)
  {
   s+=f(x);x+=h;
  }
  t2=t1/2+(h/2)*s;
  h=h/2;
 }
    return t2; 
}
void main()
{
 double a,b,c;
 cout<<"请分别输入上下限"<<endl;
 cin>>a>>b;
 cout<<"请输入误差限度："<<endl;
  cin>>c;
  cout<<ff(a,b,c)<<endl;
}