#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 200000
#define M 200000
#define N_ (N + M - 1)
int max(int a, int b) { return a > b ? a : b; }
int *el[N_], *ea[N_], eo[N_];
void append(int r, int l, int a) {
int o = eo[r]++;
if (o >= 2 && (o & o - 1) == 0) {
el[r] = (int *) realloc(el[r], o * 2 * sizeof *el[r]);
ea[r] = (int *) realloc(ea[r], o * 2 * sizeof *ea[r]);
}
el[r][o] = l, ea[r][o] = a;
}
int aa[N_], bb[N_];
int ds[N_], rr[N_]; char marked[N_]; int n, m, n_;
int find(int i) {
return ds[i] < 0 ? i : (ds[i] = find(ds[i]));
}
void join(int i, int j) {
i = find(i);
j = find(j);
if (i == j)
return;
if (ds[i] > ds[j])
ds[i] = j, rr[j] = max(rr[j], rr[i]);
else {
if (ds[i] == ds[j])
ds[i]--;
ds[j] = i, rr[i] = max(rr[i], rr[j]);
}
}
void mark(int i) {
marked[i] = 1;
if (i >= 2 && marked[i - 2])
join(i - 2, i);
if (i + 2 < n_ && marked[i + 2])
join(i, i + 2);
}
int nxt(int i) {
return !marked[i] ? i : rr[find(i)] + 2;
}
int main() {
int h, l, r, a, o;
long long ans;
scanf("%d%d", &n, &m), n_ = n + m - 1;
for (h = 0; h < n_; h++)
scanf("%d", &aa[h]);
for (h = 0; h < n_; h++)
scanf("%d", &bb[h]);
for (r = 0; r < n_; r++) {
el[r] = (int *) malloc(2 * sizeof *el[r]);
ea[r] = (int *) malloc(2 * sizeof *ea[r]);
}
for (h = 0; h < n_; h++) {
l = h < m ? m - 1 - h : h - m + 1, r = h < n ? m - 1 + h : n_ - 1 + n - 1 - h;
append(r, l, aa[h]);
}
memset(ds, -1, n_ * sizeof *ds);
for (h = 0; h < n_; h++)
rr[h] = h;
ans = 0;
for (r = 0; r < n_; r++)
for (o = eo[r]; o--; ) {
l = el[r][o], a = ea[r][o];
h = l;
while ((h = nxt(h)) <= r)
if (a >= bb[h])
a -= bb[h], ans += bb[h], bb[h] = 0, mark(h);
else {
bb[h] -= a, ans += a;
break;
}
}
printf("%lld\n", ans);
return 0;
}
