#include <cstdio>
int rectdp[51][51];
bool rectc[51][51];
int min(int a,int b){ return a>b?b:a; }
int rect(int w,int h){
if(w==h) return 1;
if(rectc[w][h]) return rectdp[w][h];
rectc[w][h]=1;
int& ret=rectdp[w][h];
ret=1e9;
int i;
for(i=1; i<w; ++i) ret=min(ret, rect(i,h)+rect(w-i,h));
for(i=1; i<h; ++i) ret=min(ret, rect(w,i)+rect(w,h-i));
return ret;
}
bool chk[51][51][51][51];
int dp[51][51][51][51];
int work(int a,int b,int c,int d){
if(a==c) {
if(b==d) return 1;
else return rect(a, b-d);
} else if(b==d){
return rect(a-c,b);
} else {
int& ret=dp[a][b][c][d];
if(chk[a][b][c][d]) return ret;
chk[a][b][c][d]=1;
ret=2e9;
int i;
for(i=1; i<=a-c; ++i) ret=min(ret, rect(i,b)+work(a-i,b,c,d));
for(i=1; i<=b-d; ++i) ret=min(ret, rect(a,i)+work(a,b-i,c,d));
for(i=1; i<c ; ++i) ret=min(ret, rect(i,b-d)+work(a-i,b,c-i,d));
for(i=1; i<d ; ++i) ret=min(ret, rect(i,a-c)+work(a,b-i,c,d-i));
return ret;
}
}
int main()
{
int a,b,c,d;
scanf("%d%d%d%d",&a,&b,&c,&d);
printf("%d\n",work(a,b,c,d));
return 0;
}
