#include <cstdio>
using namespace std;
typedef long long ll;
inline int rd(){
	int x=0;
	char c=getchar();
	while(c<'0'||c>'9')c=getchar();
	while(c>='0'&&c<='9')
		x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return x;
}
int n,k,q[500010],d[500010];
char s[1000010];
ll dp[500010],sum[500010];
inline ll upd(int f,int t){
	return dp[f]+sum[t]-sum[f]-(ll)(d[t]-d[f])*q[t]+k;
}
inline ll mmax(ll x,ll y){return x>y?x:y;}
inline ll mmin(ll x,ll y){return x<y?x:y;}
struct stk{
	int sl[500010],sr[500010],p[500010],at;
	inline void init(){at=1,sl[1]=1,sr[1]=n;}
	inline void proc(const int x){
		int l=1,r=at,mid;
		while(l<r){
			mid=l+r>>1;
			if(sr[mid]<x)l=mid+1;
			else r=mid;
		}
		dp[x]=upd(p[l],x);
	}
	inline void push(const int x){
		int lx=0;
		while(sr[at]>x){
			int u=p[at];
			if(upd(x,sr[at])>=upd(u,sr[at]))break;
			int l=mmax(x+1,sl[at]),r=sr[at],mid;
			if(upd(x,l)>upd(u,l)){--at,lx=l;continue;}
			while(l<r){
				mid=l+r>>1;
				if(upd(x,mid)<upd(u,mid))r=mid;
				else l=mid+1;
			}
			lx=l;break;
		}
		if(lx)p[++at]=x,sl[at]=lx,sr[at]=n;
	}
}ss;
int main(){
	n=rd(),k=rd();
	scanf("%s",s+1);
	int at=0,pl=0;
	for(int i=1;i<=n;++i){
		if(s[i]=='+'){
			if(!pl)++at,pl=1;
			++d[at];
		}
		else{
			if(pl)pl=0;
			++q[at];
		}
	}
	n=at-pl;
	for(int i=n-1;i>=0;--i)q[i]+=q[i+1];
	for(int i=1;i<=n;++i){
		sum[i]=sum[i-1]+(ll)d[i]*q[i];
		d[i]=d[i-1]+d[i];
	}
	ss.init();
	for(int i=1;i<=n;++i)
		ss.proc(i),ss.push(i);
	ll ans=0x3f3f3f3f3f3f3f3f;
	for(int i=0;i<=n;++i)
		ans=mmin(ans,sum[n]-sum[i]+dp[i]);
	printf("%lld\n",ans);
	return 0;
}