func_code_string: #include <bits/stdc++.h>   using namespace std;   class TwoSat {     static const int ME = 1000010;     static const int MV = 2010;     struct G {       struct E {         int u, v, next;       } e[ME];       int le, head[MV];       void init() {         le = 0;         memset(head, -1, sizeof(head));       }       void add(int u, int v) {         e[le].u = u;         e[le].v = v;         e[le].next = head[u];         head[u] = le++;       }     } g;     class Tarjan {       int Index, Bcnt, num[MV], belong[MV], dfn[MV], low[MV];       bool instack[MV];       stack<int> s;       void tarjan(int u) {         dfn[u] = low[u] = ++Index;         instack[u] = true;         s.push(u);         int v;         for (int i = g.head[u]; ~i; i = g.e[i].next) {           v = g.e[i].v;           if (!dfn[v]) {             tarjan(v);             low[u] = min(low[u], low[v]);           } else if (instack[v]) {             low[u] = min(low[u], dfn[v]);           }         }         if (dfn[u] == low[u]) {           Bcnt++;           do {             v = s.top();             s.pop();             instack[v] = false;             belong[v] = Bcnt;             num[Bcnt]++;           } while (u != v);         }       }         public:       G g;       void init() {         g.init();         Index = Bcnt = 0;         memset(num, 0, sizeof(num));         memset(dfn, 0, sizeof(dfn));         memset(low, 0, sizeof(low));         memset(instack, 0, sizeof(instack));         while (!s.empty()) s.pop();       }       void add(int u, int v) { g.add(u, v); }       void solve(int n) {         for (int i = 1; i <= n; i++) {           if (!dfn[i]) {             tarjan(i);           }         }       }       int getbcnt() { return Bcnt; }       int getbelong(int id) { return belong[id]; }       int getnum(int id) { return num[id]; }     } T;     class Unitenode {       G ug;       int n, in[MV];       bool mat[MV][MV];       queue<int> q;         public:       void init(int tn) {         n = tn;         ug.init();         memset(in, 0, sizeof(in));         for (int i = 1; i <= n; i++)           for (int j = 1; j <= n; j++) mat[i][j] = i == j ? true : false;       }       void add(int u, int v) {         if (!mat[u][v]) {           in[v]++;           mat[u][v] = true;           ug.add(u, v);         }       }       void solve(int tp[]) {         while (!q.empty()) q.pop();         for (int i = 1; i <= n; i++) {           if (!in[i]) {             q.push(i);           }         }         int ret = 1;         while (!q.empty()) {           int u = q.front();           q.pop();           tp[ret++] = u;           for (int i = ug.head[u]; ~i; i = ug.e[i].next) {             int v = ug.e[i].v;             in[v]--;             if (!in[v]) {               q.push(v);             }           }         }       }     } U;     void unite() {       U.init(T.getbcnt());       for (int i = 1; i <= n; i++) {         for (int j = T.g.head[i]; ~j; j = T.g.e[j].next) {           U.add(T.getbelong(i), T.getbelong(T.g.e[j].v));         }       }     }     int n, tp[MV];     bool flag[MV];       public:     void init(int tn) {       n = tn;       T.init();     }     void add(int u, int v) { T.add(u, v); }     bool solve() {       T.solve(n);       for (int i = 1, z = n / 2; i <= z; i++) {         if (T.getbelong(i) == T.getbelong(i + z)) return false;       }       return true;     }     void output(bool ans[]) {       unite();       U.solve(tp);       memset(flag, 0, sizeof(flag));       for (int i = T.getbcnt(); i > 0; i--) {         for (int j = 1, y; j <= n; j++) {           if (j > n / 2)             y = j - n / 2;           else             y = j;           if (!flag[y] && T.getbelong(j) == tp[i]) {             flag[y] = true;             if (j > n / 2) {               ans[j - n / 2] = true;             } else {               ans[j] = false;             }           }         }       }     }   } gx;   const int M = 128;   struct IN {     int x, y;   } in[M];   bool ok(int i, int j) {     if (in[i].x < in[j].x && in[j].x < in[i].y && in[i].y < in[j].y) return true;     return false;   }   bool judge(int i, int j) {     if (ok(i, j) || ok(j, i)) return true;     return false;   }   bool ans[M];   int main() {     int n, m;     while (~scanf( %d%d , &n, &m)) {       gx.init(m * 2);       for (int i = 1; i <= m; i++) {         scanf( %d%d , &in[i].x, &in[i].y);         if (in[i].x > in[i].y) swap(in[i].x, in[i].y);       }       for (int i = 1; i <= m; i++) {         for (int j = i + 1; j <= m; j++) {           if (judge(i, j)) {             gx.add(i, j + m);             gx.add(j, i + m);             gx.add(i + m, j);             gx.add(j + m, i);           }         }       }       if (gx.solve()) {         gx.output(ans);         for (int i = 1; i <= m; i++) {           if (ans[i])             printf( i );           else             printf( o );         }         puts(  );       } else {         puts( Impossible );       }     }     return 0;   }   