#include <bits/stdc++.h>
using namespace ::std;
const long double PI = acos(-1);
const long long MOD = 1000000000 + 7;
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long add(long long a, long long b, long long m = MOD) {
  return (a % m + b % m + 2 * m) % m;
}
long long mul(long long a, long long b, long long m = MOD) {
  return ((a % m + m) * (b % m + m)) % m;
}
long long pow_mod(long long a, long long b, long long m = MOD) {
  long long res = 1LL;
  a = a % m;
  while (b) {
    if (b & 1) res = mul(res, a, m);
    b >>= 1;
    a = mul(a, a, m);
  }
  return res;
}
long long fastexp(long long a, long long b) {
  long long res = 1LL;
  while (b) {
    if (b & 1) res = res * a;
    b >>= 1;
    a *= a;
  }
  return res;
}
int gcdExtendido(int a, int b, int *x, int *y) {
  if (a == 0) {
    *x = 0;
    *y = 1;
    return b;
  }
  int x1, y1;
  int gcd = gcdExtendido(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int modInverso(int a, int m) {
  int x, y;
  int g = gcdExtendido(a, m, &x, &y);
  if (g != 1)
    return -1;
  else
    return (x % m + m) % m;
}
const int N = 100000 + 5;
struct line {
  long long m;
  long long b;
  line(long long _m, long long _b) {
    m = _m;
    b = _b;
  }
};
int n;
int a[N];
int b[N];
long long dp[N];
vector<line> ConvexHull;
bool l2IsUseless(line l1, line l2, line l3) {
  return 1.0l * (l3.b - l1.b) * (l2.m - l1.m) >=
         1.0L * (l2.b - l1.b) * (l3.m - l1.m);
}
void add_line(line x) {
  int len = ConvexHull.size();
  while (len >= 2 and
         l2IsUseless(ConvexHull[len - 2], ConvexHull[len - 1], x)) {
    ConvexHull.pop_back();
    len--;
  }
  ConvexHull.push_back(x);
}
long long f(int i, long long x) {
  return ConvexHull[i].m * x + ConvexHull[i].b;
}
long long getMinimum(long long x) {
  int lo = 0, hi = int(ConvexHull.size()) - 1;
  while (lo < hi) {
    int mi = lo + (hi - lo) / 2;
    if (f(mi, x) >= f(mi + 1, x))
      lo = mi + 1;
    else
      hi = mi;
  }
  return f(lo, x);
}
int main() {
  scanf("%d", &(n));
  for (int i = 0; i < n; i++) {
    scanf("%d", &(a[i]));
  }
  for (int i = 0; i < n; i++) {
    scanf("%d", &(b[i]));
  }
  dp[0] = 0LL;
  add_line(line(b[0], dp[0]));
  for (int i = 1; i < n; i++) {
    dp[i] = getMinimum(a[i]);
    add_line(line(1LL * b[i], dp[i]));
  }
  printf("%lld\n", dp[n - 1]);
  return 0;
}
