n=4;
fff={{-1.,1.1},{-0.5,2.2},{0.,-1.9},{1.5,-0.7},{2.5,2.03}}

Do[x[i]=fff[[i+1]][[1]];f[i]=fff[[i+1]][[2]],{i,0,n}]

ff=Table[{x[k],f[k]},{k,0,n}]

ticks1={{0,0.2,0.4,0.6,0.8,1},{-1,0,1.2,3}};
pl1=ListPlot[ff,PlotStyle->PointSize[0.02]]

Do[d[k][0]=f[k],{k,0,n}]
Do[d[k][j]=(d[k][j-1]-d[k-1][j-1])/(x[k]-x[k-j]),{k,1,n},{j,1,k}]
pn[x_]=Sum[d[k][k]*Product[(x-x[j]),{j,0,k-1}],{k,0,n}];
pl2=Plot[pn[x],{x,-1,2.5}]

Show[pl1,pl2,PlotRange->{{-1,2.5},{-6,5.}}]