#include "stdio.h"
#include "math.h"
#define Pi 3.1415926
#define N 10
main()
{
     int k,j,n=-1,s;
     double x[N],y[N],xx,yy,t=1;
     yy=0;
     printf("enter xx:");
	 scanf("%d",&s);
	 xx=(1.0/s)*Pi;
	 printf("x=%f",xx);
	 printf("\nenter insert points:\n");
     printf("s=");
      scanf("%d",&s);
     while(s!=100)
        {
         n++;
		 x[n]=(s==0)?0:(1.0/s)*Pi;
		 y[n]=sin(x[n]);
		 printf("x%d=%f    ",n,x[n]);
		 printf("y%d=%f\n",n,y[n]);
         printf("s=");
		 scanf("%d",&s);
     	}
	 for(k=0;k<=n;k++)
	 {
		 t=1.0;
		 for(j=0;j<=n;j++)
		 {
			 if(j==k) continue;
			 else
			 t=((xx-x[j])/(x[k]-x[j]))*t;
		 }
		 yy=yy+y[k]*t;
	 }
	printf("y=%f",yy); 
	getchar();
}