1 #include <bits/stdc++.h>
 2 #define LL long long
 3 #define GG int
 4 #define For(i, j, k) for(register int i=j; i<=k; i++)
 5 #define Dow(i, j, k) for(register int i=j; i>=k; i--)
 6 using namespace std;
 7 inline GG read() {
 8     GG x = 0, f = 1;
 9     char ch = getchar();
10     while(ch<'0'||ch>'9') { if(ch=='-') f = -1; ch = getchar(); }
11     while(ch>='0'&&ch<='9') { x = x*10+ch-48; ch = getchar(); }
12     return x * f;
13 }
14 void write(GG x) {
15     if(x<0) putchar('-'), x = -x;
16     if(x>9) write(x/10);
17     putchar(x%10+48);
18 }
19 inline void writeln(GG x) { write(x); putchar('\n'); }
20
21 const int N = 2e5+11;
22 struct node{
23     int l, r, del;
24     friend bool operator <(node a, node b) {
25         if(a.del != b.del) return a.del > b.del;
26         return a.l > b.l;
27     }
28 };
29 priority_queue <node> Q;
30 int n, tot;
31 int val[N], vis[N], L[N], R[N];
32 char s[N];
33
34 inline void work() {
35     while(!Q.empty()) {
36         node p = Q.top(); Q.pop();
37         if(vis[p.l] || vis[p.r]) continue;
38         vis[p.l] = 1; vis[p.r] = 1;
39         L[++tot] = p.l; R[tot] = p.r;
40
41         int l = p.l-1, r = p.r+1;
42         while(l>=1 && vis[l]) --l;
43         while(r<=n && vis[r]) ++r;
44         if(l>=1 && r<=n && s[l]!=s[r])
45             Q.push((node){l, r, abs(val[l]-val[r]) });
46     }
47 }
48
49 int main() {
50     n = read();
51     scanf("%s", s+1);
52     For(i, 1, n) val[i] = read();
53     For(i, 1, n-1)
54         if(s[i] != s[i+1])
55             Q.push((node){i, i+1, abs(val[i]-val[i+1])} );
56     work();
57     writeln(tot);
58     For(i, 1, tot) {
59         write(L[i]); putchar(' '); writeln(R[i]);
60     }
61 }