function I=iconc(t,data);
[xx,kk]=min(abs(t-data(:,1)));
if kk<2,
    I=data(1,3)+t*(data(2,3)-data(2,1))/2;
elseif kk<24
    X=[data(kk-1,1),data(kk,1),data(kk+1,1)];
    Y=[data(kk-1,3),data(kk,3),data(kk+1,3)];
    I=Y(1)*(t-X(2))*(t-X(3))/(X(1)-X(2))/(X(1)-X(3))+Y(2)*(t-X(1))*(t-X(3))/(X(2)-X(1))/(X(2)-X(3))+Y(3)*(t-X(1))*(t-X(2))/(X(3)-X(1))/(X(3)-X(2));       
else
     I=data(23,3)+(t-data(23,1))*(data(24,3)-data(23,3))/(data(24,1)-data(23,1));
end