#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
template<class S, class T> inline S min_L(S a,T b){
  return a<=b?a:b;
}
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(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);
}
inline void wt_L(int x){
  int s=0;
  int m=0;
  char f[10];
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    my_putchar_unlocked('-');
  }
  while(s--){
    my_putchar_unlocked(f[s]+'0');
  }
}
inline void wt_L(long long x){
  int s=0;
  int m=0;
  char f[20];
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    my_putchar_unlocked('-');
  }
  while(s--){
    my_putchar_unlocked(f[s]+'0');
  }
}
int main(){
  long long N;
  long long M;
  rd(N);
  rd(M);
  if(N%2==M%2 && M%2==0){
    wt_L(0);
    wt_L('\n');
    return 0;
  }
  if(N%2==1 && M%2==0){
    wt_L(M/4);
    wt_L('\n');
    return 0;
  }
  if(N%2==0 && M%2==1){
    wt_L(N/4);
    wt_L('\n');
    return 0;
  }
  if(N%4==3 && M%4==3 &&min_L(N, M)>= 7){
    wt_L(N/4 + M/4 + 2);
    wt_L('\n');
    return 0;
  }
  if(N%2==M%2 && M%2==1){
    wt_L(N/4 + M/4);
    wt_L('\n');
    return 0;
  }
  return 0;
}
// cLay varsion 20200813-1 [beta]

// --- original code ---
// {
//   ll N, M;
//   rd(N, M);
//   if(N%2==M%2==0) wt(0), return 0;
//   if(N%2==1 && M%2==0) wt(M/4), return 0;
//   if(N%2==0 && M%2==1) wt(N/4), return 0;
//   if(N%4==3 && M%4==3 && min(N,M) >= 7) wt(N/4 + M/4 + 2), return 0;
//   if(N%2==M%2==1) wt(N/4 + M/4), return 0;
// }