请问为什么会 Unknown Error

#include <bits/stdc++.h>
using namespace std;

int x,y,n;
string s;
typedef pair<int,int> P;
map<P,bool> vis;
int main(){
	cin >> n >> s;
	for(int i=0;i<n;i++){
		if(vis[make_pair(x,y)]==true){
			cout << "Yes" << endl;
			return 0;
		}
		vis[make_pair(x,y)]=true;
		if(s[i]=='R') x++;
		else if(s[i]=='L') x--;
		else if(s[i]=='U') y++;
		else if(s[i]=='D') y--;
	}
	cout << "No" << endl;
	return 0;
}