View Compilation Error

0_0_31907099_29590.cpp:3:11: error: '::main' must return 'int'
 void main() { double x1, x2, y1, y2; double distance; while(scanf("%lf %lf %lf %lf",&x1, &y1, &x2, &y2) != EOF) {  distance = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));   printf("%.2f\n", distance); }}
           ^