//这回只花了114514min就打完了。
//真好。记得多手造几组。
#include <bits/stdc++.h>
//#define int long long
#define pai 3.141592653589793238462643383279502884197169399375105820
#define MOD 1000000007
#define eps 0.000001
inline int min(int a,int b) {return a<b?a:b;}
inline int max(int a,int b) {return a>b?a:b;}
#define ULL unsigned long long
#define LL long long
#define INF 0x3f3f3f3f
#define INF_LL 0x3f3f3f3f3f3f3f3f
static char buf[1000000],*paa=buf,*pd=buf;
static char buf2[1000000],*pp=buf2;
#define getchar() paa==pd&&(pd=(paa=buf)+fread(buf,1,1000000,stdin),paa==pd)?EOF:*paa++
inline void pc(char ch){
	if(pp-buf2==1000000) fwrite(buf2,1,1000000,stdout),pp=buf2;
	*pp++=ch;
}
inline void pcc(){
	fwrite(buf2,1,pp-buf2,stdout);
	pp=buf2;
}
inline int read(void) {
	int w=1;
	register int x(0);register char c(getchar());
	while(c<'0'||c>'9') {if(c=='-') w=-1;c=getchar();}
	while(c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return w*x;
}
void write(int x) {
	if(x<0) pc('-'),x=-x;
	static int sta[20];
	int top=0;
	do {
		sta[top++]=x%10,x/=10;
	} while(x);
	while(top) pc(sta[--top]+48);
}
void we(int x) {
	write(x);
	pc('\n');
}
inline bool cmp_xi(int a,int b) {return a<b;}
inline bool cmp_da(int a,int b) {return a>b;}
int N,M,k;
long double l1[100009],l2[100009],r1[100009],r2[100009],a[400009],su,su2[400009],qw2[400009],qw1[400009],gl1[400009],gl2[400009],ans;
bool v1[400009],v2[400009];
signed main(void) {
    //freopen("m.in","r",stdin);
    //freopen("m.out","w",stdout);
	N=read();M=read();
	a[++k]=-INF;
	a[++k]=INF;
	for(int i=1;i<=N;i++) {
		l1[i]=read();
		r1[i]=read();
		a[++k]=l1[i];
		a[++k]=r1[i]+eps;
	}
	for(int i=1;i<=M;i++) {
		l2[i]=read();
		r2[i]=read();
		a[++k]=l2[i];
		a[++k]=r2[i]+eps;
	}
	std::sort(a+1,a+k+1);
	k=std::unique(a+1,a+k+1)-a-1;
	for(int i=1;i<=N;i++) {
		int l=1,r=k,md;
		while(l<r) {
			md=(l+r)>>1;
			if(a[md]>=l1[i]) {
				r=md;
			} else {
				l=md+1;
			}
		}
		while(r1[i]>=a[l]) {
			v1[l]=1;
			l++;
		}
	}
	for(int i=1;i<=M;i++) {
		int l=1,r=k,md;
		while(l<r) {
			md=(l+r)>>1;
			if(a[md]>=l2[i]) {
				r=md;
			} else {
				l=md+1;
			}
		}
		while(r2[i]>=a[l]) {
			v2[l]=1;
			l++;
		}
	}	
	long double ssu1=0,ssu2=0;
	for(int i=1;i<k;i++) {
		if(v1[i]) ssu1+=a[i+1]-a[i];
		if(v2[i]) ssu2+=a[i+1]-a[i];
	}
	for(int i=1;i<=k;i++) a[i]=floor(a[i]);
	if(ssu1<1) {
		for(int i=1;i<k;i++) {
			gl1[i]=1;
		} 
	} else {
		for(int i=1;i<k;i++) {
			gl1[i]=a[i+1]-a[i];
		} 		
	}
	if(ssu2<1) {
		for(int i=1;i<k;i++) {
			gl2[i]=1;
		} 
	} else {
		for(int i=1;i<k;i++) {
			gl2[i]=a[i+1]-a[i];
		} 		
	}
	for(int i=1;i<k;i++) {
		su2[i]=su2[i-1];
		qw2[i]=qw2[i-1];
		if(v2[i]) su2[i]+=gl2[i],qw2[i]+=gl2[i]*(a[i+1]+a[i])/2;
		if(v1[i]) su+=gl1[i];
	}
	for(int i=k-1;i>=1;i--) {
		qw1[i]=qw1[i+1];
		if(v2[i]) qw1[i]+=gl1[i]*(a[i+1]+a[i])/2;
	}
	for(int i=1;i<k;i++) {
		if(v1[i]) {
			if(v2[i]) ans+=(a[i+1]-a[i])/3*gl1[i]*gl2[i];			
			if(su2[i-1]) ans+=((a[i]+a[i+1])/2-qw2[i-1]/su2[i-1])*gl1[i]*su2[i-1];
			if(su2[k-1]!=su2[i]) ans+=(qw1[i+1]/(su2[k-1]-su2[i])-(a[i]+a[i+1])/2)*gl1[i]*(su2[i]-su2[k-1]);
		}
	}	
	ans/=su;
	ans/=su2[k-1];
	printf("%.12Lf",ans);
    return 0;
}