/**************************************************************

     Problem: 2199

     User: zhuohan123

     Language: C++

     Result: Accepted

     Time:140 ms

     Memory:1388 kb

 ****************************************************************/

 #include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 using namespace std;

 int n,m;

 struct point{int y,n;}p[];int pnum;

 int head[];

 struct edge{int next,to;}g[];int gnum;

 void addedge(int from,int to)

 {

     g[++gnum].to=to;g[gnum].next=head[from];head[from]=gnum;

 }

 int q[],l,r;

 bool cango[];

 bool check(int po)

 {

     memset(cango,,sizeof cango);

     cango[po]=true;l=;r=;q[++r]=po;

     while(l<=r)

         for(int i=head[q[l++]];i;i=g[i].next)

             if(!cango[g[i].to])cango[q[++r]=g[i].to]=true;

     for(int i=;i<=n;i++)

         if(cango[p[i].y]&&cango[p[i].n])return false;

     return true;

 }

 char ans[];

 int main(int argc, char *argv[])

 {

     #ifndef ONLINE_JUDGE

         freopen("1.in","r",stdin);

         freopen("1.out","w",stdout);

     #endif

     scanf("%d%d",&n,&m);

     for(int i=;i<=n;i++)p[i].n=++pnum,p[i].y=++pnum;

     while(m--)

     {

         int b,c;char vb[],vc[];

         scanf("%d%s%d%s",&b,vb,&c,vc);

         if(vb[]=='Y'&&vc[]=='Y')addedge(p[b].n,p[c].y),addedge(p[c].n,p[b].y);

         if(vb[]=='Y'&&vc[]=='N')addedge(p[b].n,p[c].n),addedge(p[c].y,p[b].y);

         if(vb[]=='N'&&vc[]=='Y')addedge(p[b].y,p[c].y),addedge(p[c].n,p[b].n);

         if(vb[]=='N'&&vc[]=='N')addedge(p[b].y,p[c].n),addedge(p[c].y,p[b].n);

     }

     for(int i=;i<=n;i++)

     {

         bool by=check(p[i].y),bn=check(p[i].n);

         if(by&&bn)ans[i]='?';

         else if(by)ans[i]='Y';

         else if(bn)ans[i]='N';

         else {puts("IMPOSSIBLE");return ;}

     }

     puts(ans+);

     return ;

 }