include<stdio.h>

int main(){ int x1,y1,x2,y2,xc,yc; scanf("%d%d%d%d",&x1,&y1,&x2,&y2); xc=x1-x2; if(xc>=0){

xc=xc;

}else{

xc=xc*-1;

} yc=y1-y2; if(yc>=0){

yc=yc;

}else{

yc=yc*-1;

} printf("%d",xc+yc); return 0; }