#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
int dp[51][51];
int dp2[51][51][51][51];
int f(int h1, int w1, int h2, int w2){
if(w2 == 0 || h2 == 0){
return dp[h1][w1];
}
if(~dp2[h1][w1][h2][w2]) return dp2[h1][w1][h2][w2];
int ret = 1e9;
for(int j=1; j<h1; j++){
if(j <= h2){
ret = min(ret, dp[w1 - w2][j] + f(h1 - j, w1, h2 - j, w2));
}
else{
ret = min(ret, dp[w1][h1 - j] + f(j, w1, h2, w2));
}
}
for(int j=1; j<w1; j++){
if(j <= w2){
ret = min(ret, dp[j][h1 - h2] + f(h1, w1 - j, h2, w2 - j));
}
else{
ret = min(ret, dp[w1 - j][h1] + f(h1, j, h2, w2));
}
}
return dp2[h1][w1][h2][w2] = ret;
}
int main(){
memset(dp2,-1,sizeof(dp2));
int a, b, c, d;
scanf("%d %d %d %d",&a,&b,&c,&d);
for(int i=1; i<=50; i++){
for(int j=1; j<=50; j++){
if(i == j) dp[i][j] = 1;
else{
dp[i][j] = 1e9;
for(int k=1; k<i; k++){
dp[i][j] = min(dp[i][j], dp[k][j] + dp[i-k][j]);
}
for(int k=1; k<j; k++){
dp[i][j] = min(dp[i][j], dp[i][k] + dp[i][j-k]);
}
}
}
}
printf("%d",f(a, b, c, d));
}
