//vanitas vanitatum et omnia
#include<bits/stdc++.h>
#define fi first
#define se second
#define eb emplace_back
#define mp make_pair
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128; 
template<typename T,typename U>
T ceil(T x, U y) {return (x>0?(x+y-1)/y:x/y);}
template<typename T,typename U>
T floor(T x, U y) {return (x>0?x/y:(x-y+1)/y);}
template<class T,class S>
bool chmax(T &a,const S b) {return (a<b?a=b,1:0);}      
template<class T,class S>
bool chmin(T &a,const S b) {return (a>b?a=b,1:0);}
int popcnt(int x) {return __builtin_popcount(x);}
int popcnt(ll x)  {return __builtin_popcountll(x);}
int topbit(int x) {return (x==0?-1:31-__builtin_clz(x));}
int topbit(ll x)  {return (x==0?-1:63-__builtin_clzll(x));}
int lowbit(int x) {return (x==0?-1:__builtin_ctz(x));}
int lowbit(ll x)  {return (x==0?-1:__builtin_ctzll(x));}

#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
typedef pair<int,int> pii; 
typedef vector<int> vi;  
typedef vector<pii> vp; 
typedef tuple<int,int,int> tiii;
int read() {
  int x=0,w=1; char c=getchar(); 
  while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
  while(isdigit(c)) {x=x*10+(c-'0'); c=getchar();}
  return x*w;
}

const int N=1e6+5;
int n,m,tt,del[N];
struct node {int x,l,r;} a[N];
char s[N];
vp ans,tans;

int Del(int c,int r,int z=N,int d=0) {
  int x=c-1,y=c+1,res=0;
  rep(i,1,r) {
    while(del[x]) x--;
    while(del[y]) y++;
    pii p(a[c].l-(x+1>z)*d,a[c].r-(x+1>z)*d);
    res+=p.se-p.fi+1, ans.eb(p);
    //cout<<"D "<<c<<' '<<x<<' '<<y<<endl;
    a[c].l=a[x].l;
    a[c].r=a[x].r+a[y].r-a[y].l+1;
    del[x]=del[y]=1, x--, y++;
  } return res;
}
bool Getodd(int L,int R) {
  int n=R-L+1;
  int c=L-1+(n+1)/2,l=c,r=c,p=(n+1)/2;
  if(a[c].x==1) {
    Del(c,p-1);
    ans.eb(a[c].l,a[c].r);
    return 1;
  }
  while(l>=L&&!a[l].x) --l;
  while(r<=R&&!a[r].x) ++r;
  if(l<L||r>R) return 0;
  if(r-l>=p) return 0;
  if(r-c<=c-l) {
    int d=Del(l,r-c);
    //rep(i,1,n) if(!del[i]) cout<<i<<" "<<a[i].l<<" "<<a[i].r<<endl;
    //cout<<d<<endl;
    Del(r,p-1-(r-c),l,d);
    ans.eb(a[r].l,a[r].r);
  } else {
    Del(r,p-c); Del(l,p-1-(p-c));
    ans.eb(a[l].l,a[l].r);
  }
  return 1;
}
bool Geteven() {
  static int f[N],pre[N],suf[N],lst[N],nxt[N];
  rep(i,1,n) lst[i]=(a[i].x==1?i:lst[i-1]);
  per(i,n,1) nxt[i]=(a[i].x==1?i:nxt[i+1]);
  rep(i,1,n) if(!a[i].x) f[i]=nxt[i]-lst[i]-1;
  rep(i,1,n) if(i&1) pre[i]=min(i,f[(i+1)/2]);
  rep(i,1,n) pre[i]=(pre[i]==0||pre[i]*2+1<i);
  per(i,n,1) if((n-i+1)&1) suf[i]=min(n-i+1,f[(i+n)/2]);
  per(i,n,1) suf[i]=(suf[i]==0||suf[i]*2+1<n-i+1);
  rep(i,1,n) if((i&1)&&pre[i]&&suf[i+1]) {
    //cout<<i<<endl;
    Getodd(i+1,n), Getodd(1,i);
    return 1;
  } return 0;
}

signed main() {
  scanf("%d%s",&n,s+1);
  rep(i,1,n) {
    int l=i, r=i;
    while(r<=n&&s[r]==s[l]) r++; r--;
    //cout<<l<<" "<<r<<endl;
    a[++m]=(node){l!=r,l,r}; i=r;
  }
  n=m;
  //rep(i,1,n) cout<<a[i].x<<" "; puts("");
  if(n&1) tt=Getodd(1,n);
  else tt=Geteven();
  if(!tt) puts("-1");
  for(auto [l,r]:ans) {
    if((r-l)&1) {
      for(int x=r-1;x>=l;x-=2) tans.eb(x,x+1);
    } else {
      tans.eb(r-2,r);
      for(int x=r-4;x>=l;x-=2) tans.eb(x,x+1);
    }
  }
  printf("%d\n",(int)tans.size());
  for(auto [l,r]:tans) printf("%d %d\n",l,r);
  return 0;
}