Gym 101848G

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll long long
#define db double

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c)){x=x*10+c-'0';gc;}x*=k;
}

const int N=5e5+7;

int t[N];
int y[N];
db f[N];
db tag[N];

int main(){
    // freopen(".in","r",stdin);
    // freopen(".out","w",stdout);
    int n,h;r(n),r(h);
    for(int i=1;i<=n;++i){
        r(t[i]),r(y[i]);
        y[i]+=1e5;
    }
    y[0]=1e5;
    for(int i=1;i<=n;++i){
        int l=min(y[i-1],y[i]);
        int r=max(y[i-1],y[i]);
        if(l==r){
            tag[l]+=(t[i]-t[i-1]);
            continue;
        }
        db w=(t[i]-t[i-1])/(db)(r-l);
        f[l+1]+=w;
        f[r+1]-=w;
    }
    for(int i=1;i<=2e5+h;++i)f[i]+=f[i-1];
    db sum=0;
    for(int i=0;i<=h;++i){
        sum+=f[i]+tag[i];
    }
    db ans=sum;
    for(int i=1;i<=2e5;++i){
        // printf("l=%d, r=%d, sum=%.8lf\n",i,i+h,f[i+h]-f[i]);
        sum-=f[i]+tag[i-1];
        sum+=f[i+h]+tag[i+h];
        ans=max(ans,sum);
    }
    printf("%.8lf\n",ans);
    return 0;
}
/*
3 2
50 0
75 2
100 2
*/