#include<bits/stdc++.h>
#define N 1000005
#define re 
#define ll long long
using namespace std; 
int n,m,K,q,T;
inline void Rd(int &res){
	re char c;res=0;
	while(c=getchar(),c<48);
	do res=(res<<3)+(res<<1)+(c^48);
	while(c=getchar(),c>47);
}
int Y;
ll f[N];
ll sum1[N],sum2[N],sum0[N];
struct node{
	ll k,b;
	ll calc(ll x){return k*x+b;}
}V[N<<2];
bool mk[N<<2];
void update(int l,int r,node res,int p){
	if(!mk[p]){
		mk[p]=1;V[p]=res;
		return;
	}
	if(l==r){
		if(V[p].calc(l)<res.calc(l))V[p]=res;
		return;
	}
	int mid=(l+r)>>1;
	if(V[p].k>res.k){
		if(V[p].calc(mid)<res.calc(mid)){
			update(mid+1,r,V[p],p<<1|1);
			V[p]=res;
		}
		else update(l,mid,res,p<<1);
	}
	else{
		if(V[p].calc(mid)<res.calc(mid)){
			update(l,mid,V[p],p<<1);
			V[p]=res;
		}
		else update(mid+1,r,V[p],p<<1|1);
	}
}
ll query(int l,int r,int x,int p){
	if(!mk[p])return -1e18;
	if(l==r)return V[p].calc(x);
	int mid=(l+r)>>1;
	if(x<=mid)return max(V[p].calc(x),query(l,mid,x,p<<1));
	else return max(V[p].calc(x),query(mid+1,r,x,p<<1|1));
}
char c[N];
int main(){
	Rd(n);Rd(Y);
	scanf("%s",c+1);
	for(re int i=1;i<=n;i++){
		sum0[i]=sum0[i-1],sum1[i]=sum1[i-1],sum2[i]=sum2[i-1];
		if(c[i]=='+')sum1[i]++;
		else sum2[i]++,sum0[i]+=sum1[i];
	}
	
	int i=0;
	f[0]=0;
	ll k=-sum1[i];
	ll b=f[i]-sum0[i]+sum2[i]*sum1[i];
	
	k=-k,b=-b;
	node now=(node){k,b};
	update(0,n,now,1);
	
	for(re int i=1;i<=n;i++){
		ll x=sum2[i];
		ll res=-query(0,n,x,1);
		f[i]=res+sum0[i]+Y;
		
		
		ll k=-sum1[i];
		ll b=f[i]-sum0[i]+sum2[i]*sum1[i];
		
		k=-k,b=-b;
		node now=(node){k,b};
		update(0,n,now,1);
	}
	printf("%lld\n",f[n]-Y);
	
	
	
	
	
	return 0;
}