#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
double ans=99999999999999.0;
struct Point{int x,y;Point(const int &x,const int &y){this->x=x;this->y=y;}Point(){}double Length(){return sqrt((double)x*(double)x+(double)y*(double)y);}void read(){scanf("%d%d",&x,&y);}
}p[105];
typedef Point Vector;
Vector operator - (const Point &a,const Point &b){return Vector(a.x-b.x,a.y-b.y);
}
int Dot(const Vector &a,const Vector &b){return a.x*b.x+a.y*b.y;
}
int Cross(const Vector &a,const Vector &b){return a.x*b.y-a.y*b.x;
}
int n,m,K;
double DisToSegment(Point P,Point A,Point B)
{Vector v1=B-A,v2=P-A,v3=P-B;if(Dot(v1,v2)<=0) return v2.Length();else if(Dot(v1,v3)>0) return v3.Length();else return fabs((double)Cross(v1,v2))/v1.Length();
}
double Min(double a,double b,double c,double d,double e){return min(a,min(b,min(c,min(d,e))));
}
//double Min(double a,double b,double c){
//  return min(a,min(b,c));
//}
int main(){freopen("input.txt","r",stdin);freopen("output.txt","w",stdout);scanf("%d%d%d",&n,&m,&K);for(int i=0;i<n;++i){p[i].read();}if(m+K==n+4){if(m==3 || m==n+1){puts("0.000");return 0;}for(int i=0;i<n;++i){int j=(i+m-2)%n;ans=Min(ans,DisToSegment(p[i],p[j],p[(j+1)%n]),DisToSegment(p[(i+1)%n],p[j],p[(j+1)%n]),DisToSegment(p[j],p[i],p[(i+1)%n]),DisToSegment(p[(j+1)%n],p[i],p[(i+1)%n]));}printf("%.3lf\n",ans);}else if(m+K==n+3){for(int i=0;i<n;++i){int j=(i+m-2)%n;ans=min(ans,DisToSegment(p[i],p[j],p[(j+1)%n]));j=(i-(m-2)+n)%n;ans=min(ans,DisToSegment(p[i],p[j],p[(j-1+n)%n]));}printf("%.3lf\n",ans);}else if(m+K==n+2){for(int i=0;i<n;++i){int j=(i+m-1)%n;ans=min(ans,(p[i]-p[j]).Length());j=(i-(m-1)+n)%n;ans=min(ans,(p[i]-p[j]).Length());}printf("%.3lf\n",ans);}else{puts("-1");}return 0;
}