dcva

//Nguyen Huu Hoang Minh
#include <bits/stdc++.h>
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define reset(x) memset(x, 0,sizeof(x))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define N 100005
#define remain(x) if (x > MOD) x -= MOD
#define ii pair<int, int>
#define iiii pair< ii , ii >
#define viiii vector< iiii >
#define vi vector<int>
#define vii vector< ii >
#define bit(x, i) (((x) >> (i)) & 1)
#define Task "test"
#define int long long

using namespace std;

typedef long double ld;
typedef int ftype;
typedef complex<ftype> point;
const int inf = 1e10;
const int minf = -1e10;
#define x real
#define y imag

vector<point> hull, vecs;

ftype cross(point a, point b){
    return (conj(a)*b).imag();
}

ftype dot(point a, point b){
    return (conj(a)*b).real();
}

void add_line(ftype k, ftype b){
    point nw = {k,b};
    //dot > 0 -> k giam dan
    //dot < 0 -> k tang dan
    while (vecs.size() && dot(vecs.back(),(nw-hull.back()))>0){
        vecs.pop_back();
        hull.pop_back();
    }
    if (hull.size()){
        vecs.push_back(point(1i)*(nw-hull.back()));
    }
    hull.push_back(nw);
}

ftype get(ftype x){
    point q = {x,1};
    auto it = lower_bound(vecs.begin(),vecs.end(),q,
    [](point a, point b){
            return cross(a,b)>0;
    });
    //min cross > 0
    //max cross < 0
    return dot(q,hull[it-vecs.begin()]);
}

int n,c;
int dp[N], a[N], b[N];

void readfile()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    if (fopen(Task".inp","r"))
    {
        freopen(Task".inp","r",stdin);
        //freopen(Task".out","w",stdout);
    }
    cin >> n >> c;
    for(int i=1; i<=n; i++) cin >> a[i];
    for(int i=1; i<=n; i++) cin >> b[i];
}

void proc()
{
    dp[1] = c;
    add_line(b[1],dp[1]);
    int Min = dp[1];
    for(int i=2; i<=n; i++){
        dp[i] = get(a[i]);
        if (b[i]<b[i-1] || (b[i]==b[i-1] && dp[i]<Min)) add_line(b[i],dp[i]);
    }
    cout << dp[n];
}

signed main()
{
    readfile();
    proc();
    return 0;
}