#include<stdio.h>
#include<math.h>
void main()
{
	float xy[2][11],x,y=0,h;
	int n,i,j,k;
    char flag='y';
	printf("input n,max[n]=10\n");
	scanf("%d",&n);
	printf("input x[i],y[i]:\n");
    printf("input x[i]:\n");
    for(j=0;j<=n;j++)
	scanf("%f",&xy[0][j]);
    printf("input y[i]:\n");
    for(j=0;j<=n;j++)
	scanf("%f",&xy[1][j]);
	h=(xy[0][n]-xy[0][0])/n;

      getchar();
printf("please enter 'y' to start:\n");
for(;flag==getchar();)
{

    printf("input x:\n");
	scanf("%f",&x);


    if(x-xy[0][1]<0)i=1;
	else if(x-xy[0][n-1]>=0)i=n-1;
	else for(i=1;i<=n-1;i++)
	     if(fabs(x-xy[0][i])<=0.5*h)break;






/*
for(k=i-1;k<=i+1;k++)
{float fz=1,fm=1;
for(j=i-1;j<=i+1;j++)
if(j!=k)
{fz*=x-xy[0][j];
fm*=xy[0][k]-xy[0][j];
}
y=y+xy[1][k]*fz/fm;
}
*/



y=xy[1][i-1]*(x-xy[0][i])*(x-xy[0][i+1])/((xy[0][i-1]-xy[0][i])*(xy[0][i-1]-xy[0][i+1]));
y=y+xy[1][i]*(x-xy[0][i-1])*(x-xy[0][i+1])/((xy[0][i]-xy[0][i-1])*(xy[0][i]-xy[0][i+1]));
y=y+xy[1][i+1]*(x-xy[0][i-1])*(x-xy[0][i])/((xy[0][i+1]-xy[0][i-1])*(xy[0][i+1]-xy[0][i]));


printf("output y:\n");
printf("%f",y);

 getchar();
printf("\nplease enter 'y' to continue:\n");

}
}