#include <stdio.h>
int main(){
int a,b,c,d=0;
scanf("%d%d%d",&b,&a,&c);
printf("%d\n",(a?a>0?(a-1)/c:~a/c+1:-1)+(b?b>0?(b-1)/c:~b/c:-1)+3-(a>0&&!b)-(!a&!b));
return 0;
}