#include<bits/stdc++.h>
#define For(i,a,b) for(register int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(register int i=(a);i>=(b);--i)
#define int long long
using namespace std;
inline int read()
{
    char c=getchar();int x=0;bool f=0;
    for(;!isdigit(c);c=getchar())f^=!(c^45);
    for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
    if(f)x=-x;return x;
}

#define mod  998244353 
#define inv2 499122177
struct modint{
    int x;
    modint(int o=0){x=(o%mod+mod)%mod;}
    modint &operator = (int o){return x=o,*this;}
    modint &operator +=(modint o){return x=x+o.x>=mod?x+o.x-mod:x+o.x,*this;}
    modint &operator -=(modint o){return x=x-o.x<0?x-o.x+mod:x-o.x,*this;}
    modint &operator *=(modint o){return x=1ll*x*o.x%mod,*this;}
    modint &operator ^=(int b){
        modint a=*this,c=1;
        for(;b;b>>=1,a*=a)if(b&1)c*=a;
        return x=c.x,*this;
    }
    modint &operator /=(modint o){return *this *=o^=mod-2;}
    modint &operator +=(int o){return x=x+o>=mod?x+o-mod:x+o,*this;}
    modint &operator -=(int o){return x=x-o<0?x-o+mod:x-o,*this;}
    modint &operator *=(int o){return x=1ll*x*o%mod,*this;}
    modint &operator /=(int o){return *this *= ((modint(o))^=mod-2);}
    template<class I>friend modint operator +(modint a,I b){return a+=b;}
    template<class I>friend modint operator -(modint a,I b){return a-=b;}
    template<class I>friend modint operator *(modint a,I b){return a*=b;}
    template<class I>friend modint operator /(modint a,I b){return a/=b;}
    friend modint operator ^(modint a,int b){return a^=b;}
    friend bool operator ==(modint a,int b){return a.x==b;}
    friend bool operator !=(modint a,int b){return a.x!=b;}
    bool operator ! () {return !x;}
    modint operator - () {return x?mod-x:0;}
};
inline modint qpow(modint x,int y){return x^y;}
#define maxn 400005
int n,m;
char str[maxn];
modint fac[maxn],ifac[maxn];
inline modint C(int n,int m){
	if(n<0||m<0||n<m)return 0;
	return fac[n]*ifac[m]*ifac[n-m];
}
void prework(int n){
	fac[0]=ifac[0]=1;
	For(i,1,n)fac[i]=fac[i-1]*i,ifac[i]=ifac[i-1]/i;
}
inline modint sign(int x){return (x&1)?(mod-1):(1);}

// sum(C(n,i)) 0<=i<=t
struct node{
	int n,t;
	modint res=1;
	void N(int op){
		if(op==1){
			res*=2,res-=C(n,t),++n;
			if(n==0)res=(t>=0);
		}else{
			if(n==0)res=0;
			n--,res+=C(n,t),res*=inv2;
		}
	}
	void T(int op){
		if(op==1)res+=C(n,t+1),++t;
		else res-=C(n,t),--t;
	}
}f1,f2,f3,f4;

int cnt,t;
void tup(int p){
	//if(p==1)puts("tup");else puts("tdown");
	f1.T(p),f2.T(p),t+=p;
}
void cntup(int o){
//	if(o==1)puts("cntup");else puts("cntdown");
	f1.N(o),f2.N(o),f3.N(o),f4.N(o);
	f3.T(o),f4.T(o),cnt+=o;
}

modint solve()
{
	modint res=0;
	if(cnt==1)
	{
		For(i,0,cnt)
			if((t+i)%2==0)res+=1ll*abs(t-i)*C(cnt,i);
		return res*inv2;
	}
//	cout<<f1.t<<' '<<f2.t<<' '<<f3.t<<' '<<f4.t<<endl;
	res+=modint(t)*2*f1.res;
	res-=modint(cnt)*2*f2.res;
	res+=modint(cnt)*f3.res;
	res-=modint(t)*f4.res;
	res*=qpow(inv2,cnt);
	return res;
}

signed main()
{
	n=read(),m=read(),prework(n);cin>>(str+1);
	f1.N(-1),f2.N(-1),f2.N(-1),f3.N(-1),f3.N(-1),f4.N(-1);
	f2.T(-1),f3.T(-1);
	For(i,1,n){
		if(str[i]=='b')tup(i%2?-1:1);
		else if(str[i]=='?'){
			cntup(1);
			if(i%2==0)tup(1);
		}
	}
	printf("%d\n",solve().x);
	while(m--)
	{
		int x=read();
		char ch;cin>>ch;
		if(ch=='b')tup(x%2?-1:1);
		else if(ch=='?'){
			cntup(1);
			if(x%2==0)tup(1);
		}
		if(str[x]=='b')tup(x%2?1:-1);
		else if(str[x]=='?'){
			cntup(-1);
			if(x%2==0)tup(-1);
		}
		str[x]=ch;
		printf("%d\n",solve().x);
	}
    return 0;
}