function pitch_marks = find_pmark(speech)
 N=320;%the lengh of samples in frame
 
 for k=1:N%auto correlation
     R(k)=0;
     for i=1:N-k
     R(k)=R(k)+speech(i)*speech(i+k-1);
     end
 end

 t=0;
 for k=20:N%歸一并計算候選
     if(R(k)/R(1)>=0.2)
         t=t+1;
         m(t)=k;
        
     end
 end

 for i=1:t-2
    dis(i)=0;
     for j=i+1:t%?
         dis(i)=dis(i)+near_mod(m(j),m(i))/(t+1-i);
     end
 end

 ma=dis(1);
 max=1;
 for i=1:t-2
     if(m>dis(i))
         m=dis(i);
         max=i;
     end
 end

 pitch_marks=m(max);