#include <bits/stdc++.h>   using namespace std;   const int inf = 1000018;   char str[2][510000], text[1010000];   int n, ans[1010000], num_node, fail[1010000], nxt[1010000], len[1010000],       to[1010000][26], path[1010000], pa[1010000];   int dl[1010000], last, save[1010000], ie[1010000];   void init() {     num_node = 2;     fail[0] = 1;     len[1] = -1;     len[0] = 0;     nxt[0] = 1;     last = 0;   }   int get_fail(int id, int pos) {     while (pos - len[id] - 1 < 1 || text[pos - len[id] - 1] != text[pos])       id = fail[id];     return id;   }   void add_letter(int pos) {     int cur = get_fail(last, pos);     if (!to[cur][text[pos] -  a ]) {       len[num_node] = len[cur] + 2;       fail[num_node] = to[get_fail(fail[cur], pos)][text[pos] -  a ];       dl[num_node] = len[num_node] - len[fail[num_node]];       if (dl[num_node] == dl[fail[num_node]])         nxt[num_node] = nxt[fail[num_node]];       else         nxt[num_node] = fail[num_node];       to[cur][text[pos] -  a ] = num_node++;     }     last = to[cur][text[pos] -  a ];   }   int main() {     scanf( %s%s , str[0], str[1]);     n = strlen(str[0]);     int i, j, s, p, q;     for (i = 0; i < n; i++) {       text[2 * i] = str[0][i];       text[2 * i + 1] = str[1][i];     }     n *= 2;     for (i = n - 1; i >= 0; i--) text[i + 1] = text[i];     init();     for (i = 1; i <= n; i++) {       add_letter(i);       ans[i] = inf;       for (j = last; len[j] > 0; j = nxt[j]) {         save[j] = ans[i - len[nxt[j]] - dl[j]];         path[j] = i - len[nxt[j]] - dl[j];         if (dl[j] == dl[fail[j]]) {           if (save[j] > save[fail[j]]) {             save[j] = save[fail[j]];             path[j] = path[fail[j]];           }         }         if (!(i & 1)) {           if (ans[i] > save[j] + 1) {             ans[i] = save[j] + 1;             pa[i] = path[j];           }         }       }       if (!(i & 1) && text[i] == text[i - 1]) {         if (ans[i] > ans[i - 2]) {           ans[i] = ans[i - 2];           pa[i] = i - 2;         }       }     }     if (ans[n] == inf)       puts( -1 );     else {       printf( %d n , ans[n]);       int id = n;       while (id > 0) {         if (pa[id] + 2 != id) printf( %d %d n , pa[id] / 2 + 1, id / 2);         id = pa[id];       }     }     return 0;   }   