#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
void*wmem;
char memarr[96000000];
template<class T> inline void walloc1d(T **arr, int x, void **mem = &wmem){
  static int skip[16] = {0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  (*mem) = (void*)( ((char*)(*mem)) + skip[((unsigned long long)(*mem)) & 15] );
  (*arr)=(T*)(*mem);
  (*mem)=((*arr)+x);
}
template<class T> inline void walloc1d(T **arr, int x1, int x2, void **mem = &wmem){
  walloc1d(arr, x2-x1, mem);
  (*arr) -= x1;
}
template<class T1> void sortA_L(int N, T1 a[], void *mem = wmem){
  sort(a, a+N);
}
inline int my_getchar_unlocked(){
  static char buf[1048576];
  static int s = 1048576;
  static int e = 1048576;
  if(s == e && e == 1048576){
    e = fread_unlocked(buf, 1, 1048576, stdin);
    s = 0;
  }
  if(s == e){
    return EOF;
  }
  return buf[s++];
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
inline void rd(long long &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
struct MY_WRITER{
  char buf[1048576];
  int s;
  int e;
  MY_WRITER(){
    s = 0;
    e = 1048576;
  }
  ~MY_WRITER(){
    if(s){
      fwrite_unlocked(buf, 1, s, stdout);
    }
  }
}
;
MY_WRITER MY_WRITER_VAR;
void my_putchar_unlocked(int a){
  if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){
    fwrite_unlocked(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout);
    MY_WRITER_VAR.s = 0;
  }
  MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a;
}
inline void wt_L(char a){
  my_putchar_unlocked(a);
}
int WRITER_DOUBLE_DIGIT = 15;
inline int writerDigit_double(){
  return WRITER_DOUBLE_DIGIT;
}
inline void writerDigit_double(int d){
  WRITER_DOUBLE_DIGIT = d;
}
inline void wt_L(double x){
  const int d = WRITER_DOUBLE_DIGIT;
  int k;
  int r;
  double v;
  if(x!=x || (x==x+1 && x==2*x)){
    my_putchar_unlocked('E');
    my_putchar_unlocked('r');
    my_putchar_unlocked('r');
    return;
  }
  if(x < 0){
    my_putchar_unlocked('-');
    x = -x;
  }
  x += 0.5 * pow(0.1, d);
  r = 0;
  v = 1;
  while(x >= 10*v){
    v *= 10;
    r++;
  }
  while(r >= 0){
    r--;
    k = floor(x / v);
    if(k >= 10){
      k = 9;
    }
    if(k <= -1){
      k = 0;
    }
    x -= k * v;
    v *= 0.1;
    my_putchar_unlocked(k + '0');
  }
  if(d > 0){
    my_putchar_unlocked('.');
    v = 1;
    for(r=(0);r<(d);r++){
      v *= 0.1;
      k = floor(x / v);
      if(k >= 10){
        k = 9;
      }
      if(k <= -1){
        k = 0;
      }
      x -= k * v;
      my_putchar_unlocked(k + '0');
    }
  }
}
template<class T> long long counterProdIsLT(int As, T A[], int Bs, T B[], T val){
  int i;
  int j;
  int ma = 0;
  int za = 0;
  int pa = 0;
  int mb = 0;
  int zb = 0;
  int pb = 0;
  long long res = 0;
  i = 0;
  while(i < As && A[i] < 0){
    i++;
  }
  ma = i;
  while(i < As && A[i] == 0){
    i++;
  }
  za = i - ma;
  pa = As - i;
  i = 0;
  while(i < Bs && B[i] < 0){
    i++;
  }
  mb = i;
  while(i < Bs && B[i] == 0){
    i++;
  }
  zb = i - mb;
  pb = Bs - i;
  if(val < 0){
    j = 0;
    for(i=(0);i<(pa);i++){
      while(j < mb && A[As-pa+i] * B[j] < val){
        j++;
      }
      res += j;
    }
    j = 0;
    for(i=(0);i<(pb);i++){
      while(j < ma && B[Bs-pb+i] * A[j] < val){
        j++;
      }
      res += j;
    }
  }
  else if(val == 0){
    res = (long long) ma * pb + (long long) pa * mb;
  }
  else{
    res = (long long) As * Bs - (long long) pa * pb - (long long) ma * mb;
    j = pb;
    for(i=(0);i<(pa);i++){
      while(j && A[As-pa+i] * B[Bs-pb+j-1] >= val){
        j--;
      }
      if(j==0){
        break;
      }
      res += j;
    }
    j = mb;
    for(i=(0);i<(ma);i++){
      while(j && A[ma-1-i] * B[mb-j] >= val){
        j--;
      }
      if(j==0){
        break;
      }
      res += j;
    }
  }
  return res;
}
int N;
int M;
long long C;
long long A[100000];
long long B[100000];
int main(){
  wmem = memarr;
  double res;
  rd(N);
  rd(M);
  rd(C);
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=(0);Lj4PdHRW<(N);Lj4PdHRW++){
      rd(A[Lj4PdHRW]);
    }
  }
  {
    int e98WHCEY;
    for(e98WHCEY=(0);e98WHCEY<(M);e98WHCEY++){
      rd(B[e98WHCEY]);
    }
  }
  sortA_L(N, A);
  sortA_L(M, B);
  res = 1 - (double)counterProdIsLT(N, A, M, B, C+1) / N / M;
  wt_L(res);
  wt_L('\n');
  return 0;
}
// cLay varsion 20201102-1

// --- original code ---
// int N, M; ll C, A[1d5], B[1d5];
// {
//   double res;
//   rd(N,M,C,A(N),B(M));
//   sortA(N, A);
//   sortA(M, B);
//   res = 1 - (double)counterProdIsLT(N, A, M, B, C+1) / N / M;
//   wt(res);
// }