ACM小题，错哪里？

                                                                            
[解决办法]
开根号是sqrt.


#include <iostream>
#include <math.h>

using namespace std;

int main()
{  
float x1,y1,x2,y2;
cin>>x1>>y1>>x2>>y2;
float s=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
s = sqrt(s);
cout.precision(2);
cout<<fixed<<s<<endl;
return 0;
}