#include<stdio.h>
#include<math.h>
#define SIZE 200

int main(void)
{
FILE *fin;
int i, N;
double x[SIZE], y[SIZE];
double xbuf, ybuf, rbuf;
double xheikin, yheikin;
double xhensa, yhensa;
double r;

fin = fopen("xy_data", "r");
do {
fscanf(fin, "%lf %lf", &x[i++], &y[i++]);
} while ( !feof(fin) );
fclose(fin);
N = i;

xbuf = 0.0, ybuf = 0.0;
for(i=0 ; i<N ; i++) {
xbuf += x[i];
ybuf += y[i];
}
xheikin = xbuf / N;
yheikin = ybuf / N;