ll@n,@m,@a[m],b[m],d[m],x=0;
d[0..m-1]=ll_inf;
rep(f,1,n){
	rd(b(m));
	rep(j,m){
		d[j]=min(d[j],x+a[j])+b[j];
		a[j]=b[j];
	}
	x=min(d(m));
}
wt(x);