for(int l = 0; l < n; l++) {
int pl = (l + n - 1)%n, nl = (l + 1)%n;
if(xt[nl] - xt[l] != xt[l] - xt[pl] || yt[nl] - yt[l] != yt[l] - yt[pl]) {
for(int l = 0; l < n; l++) {
int pl = (l + n - 1)%n, nl = (l + 1)%n;
if(xt[nl] - xt[l] != xt[l] - xt[pl] || yt[nl] - yt[l] != yt[l] - yt[pl]) {