#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;const int N=2005,M=2e5+5;typedef long long ll;inline int read(){    char c=getchar();int x=0,f=1;    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}    return x*f;}inline void get(int &x,char &c){    c=getchar();    while(c!=‘h‘&&c!=‘m‘) c=getchar();    x=read()<<1;}int n,m,x,y,vx,vy;char s[3];struct edge{    int v,ne;}e[M];int h[N],cnt=0;inline void ins(int u,int v){    cnt++;    e[cnt].v=v;e[cnt].ne=h[u];h[u]=cnt;}bool mark[N];bool dfs(int u){    if(mark[u^1]) return false;    if(mark[u]) return true;    mark[u]=1;    for(int i=h[u];i;i=e[i].ne)        if(!dfs(e[i].v)) return false;    return true;}bool check(int u){    memset(mark,0,sizeof(mark));    return dfs(u);}char ans[N];int main(){    freopen("in","r",stdin);    n=read();m=read();    for(int i=1;i<=m;i++){        x=read()<<1;scanf("%s",s);vx=s[0]==‘Y‘;        y=read()<<1;scanf("%s",s);vy=s[0]==‘Y‘;        x|=vx;y|=vy;        ins(x^1,y);ins(y^1,x);    }    for(int i=1;i<=n;i++){        int p=check(i<<1),q=check(i<<1|1);        if(!p&&!q){puts("IMPOSSIBLE");return 0;}        else if(p&&q) ans[i]=‘?‘;        else if(q) ans[i]=‘Y‘;        else ans[i]=‘N‘;    }    for(int i=1;i<=n;i++) putchar(ans[i]);}