include<stdio.h>//本题答案

int main() {

int x1,x2,y1,y2,x,y,d;
x=0;
y=0;
d=0;
scanf("%d %d %d %d",&x1,&y1,&x2,&y2);
x=x1-x2;
if(x<0){
    x*=-1;
}
y=y1-y2;
if(y<0){
    y*=-1;
}
d=x+y;
printf("%d",d);
return 0;

}