a,b,c,d,s,t;main(){scanf("%d%d%d%d",&d,&a,&b,&c);if((a<b&c<b|a>b&c>b)&&a-c&&puts("0")||!d&&puts("-1"))exit(0);a>c?a^=c^=a^=c:a==c?s++,a=a<d?0:a-d:0;t=(c-b)/d+1;t=a|t*d<c?t+s+(t*d+a==c):-1;c=(b-a)/d+1;a=!printf("%d",a|c*d<b&&c<t?c+s:t);}