#include<iostream>
#include<string>
#include<cstdio>
using namespace std;
string s1,s2;
int a[10100],b[10100],la,lb,lc;
int main(){
	cin>>s1>>s2;
	la=s1.size();
	lb=s2.size();
	if(la<lb||la==lb&&s1<s2){
		string s3;
		s3=s1;
		s1=s2;
		s2=s3;
		lc=la;
		la=lb;
		lb=lc;
		cout<<"-";
	}
	else if(s1==s2){
		cout<<0;
		return 0;
	}
	for(int i=0;i<la;i++){
		a[i]=s1[la-i]-'0';
	}
	for(int i=0;i<lb;i++){
		a[i]=s1[la-i]-'0';
	}
	for(int i=1;i<=la;i++){
		if(a[i]<b[i]){
			a[i+1]--;
			a[i]+=10;
		}
		a[i]=a[i]-b[i];
	}
	while(a[la]==0&&la>0){
		la--;
	}
	for(int i=la;i>=1;i--){
		cout<<a[i];
	} 
}

就十分，求助！！