#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>

using namespace std;

const int maxm=20001;
const int maxn=3001;
int n,m;
inline int op(int x)
{
	return x>n ? x-n : x+n;
}

struct edge
{
	int t,o;
	edge *next;
}E[maxm],*V[maxn];
int eh;
inline void addedge(int a,int b)
{
	E[++eh].next=V[a];  V[a]=E+eh;  V[a]->t=b;
}

void init()
{
	char st[11];
	int t1,t2;
	scanf("%d%d",&n,&m);
	for (int i=1;i<=m;i++)
	{
		scanf("%d%s",&t1,st);
		if (st[0]=='N') t1+=n;
		scanf("%d%s",&t2,st);
		if (st[0]=='N') t2+=n;
		addedge(op(t1),t2);
		addedge(op(t2),t1);
	}
}

int stack[maxn],dfn[maxn],low[maxn],bel[maxn],sh,bcnt,indexdfn;
bool instack[maxn];
void tarjan(int u)
{
	dfn[u]=low[u]=++indexdfn;
	stack[++sh]=u;
	instack[u]=true;
	int v;
	for (edge *e=V[u];e;e=e->next)
	{
		v=e->t;
		if (!dfn[v])
		{
			tarjan(v);
			if (low[u]>low[v]) low[u]=low[v];
		}
		else if (instack[v] && low[u]>dfn[v])
			low[u]=dfn[v];
	}
	if (dfn[u]==low[u])
	{
		++bcnt;
		do
		{
			v=stack[sh--];
			instack[v]=false;
			bel[v]=bcnt;
		}while (u!=v);
	}
}

edge newE[maxm],*newV[maxn];
int neweh;

inline void addnewedge(int a,int b)
{
	newE[++neweh].next=newV[a];  newV[a]=newE+neweh;  newV[a]->t=b;  newV[a]->o=1;
	newE[++neweh].next=newV[b];  newV[b]=newE+neweh;  newV[b]->t=a;  newV[b]->o=2;
}

int color[maxn],tcolor[maxn];

bool dfs(int u,int o)
{
	color[u]=o;
	for (int i=1;i<=2*n;i++)
	if (bel[i]==u)
	{
		if (!color[bel[op(i)]] && !dfs(bel[op(i)],3-o)) return false;
		if (color[bel[op(i)]] && color[bel[op(i)]]==color[u]) return false;
	}
	for (edge *e=newV[u];e;e=e->next)
	if (e->o==o)
	{
		if (!color[e->t] && !dfs(e->t,o)) return false;
		if (color[e->t] && color[e->t]!=color[u]) return false;
	}
	return true;
}

void cul(int u)
{
	memcpy(tcolor,color,sizeof(color));
	if (dfs(u,1))
	{
		memcpy(color,tcolor,sizeof(tcolor));
		if (dfs(u,2)) tcolor[u]=0;
		else tcolor[u]=1;
	}
	else tcolor[u]=2;
	memcpy(color,tcolor,sizeof(tcolor));
}

void solve()
{
	for (int i=1;i<=2*n;i++)
	if (!dfn[i]) tarjan(i);
	
	for (int i=1;i<=n;i++)
	if (bel[i]==bel[op(i)])
	{
		printf("IMPOSSIBLE\n");
		return ;
	}
	
	memset(newV,0,sizeof(newV));
	for (int u=1;u<=2*n;u++)
	for (edge *e=V[u];e;e=e->next)
	if (bel[u]!=bel[e->t])
	{
		addnewedge(bel[u],bel[e->t]);
	}
	
	for (int i=1;i<=bcnt;i++) cul(i);
	
	for (int i=1;i<=n;i++)
	{
		if (color[bel[i]]==1) printf("Y");
		else if (color[bel[i]]==2) printf("N");
		else printf("?");
	}
	printf("\n");
	
}

int main()
{
	freopen("cowngress.in","r",stdin);
	freopen("cowngress.out","w",stdout);
	init();
	solve();
	return 0;
}