#include <stdio.h>
int main() {
double n,a, maxV, v;
// int arr[100] = {0};
long long int tempV;
int found = 0,i;
scanf("%lf %lf", &n, &a);
printf("%0.lf ", n-a);
i=1;
while (found==0 && v<n) {
v=(i/a*n)+(1/a);
tempV = v;
// printf("v: %lf\n", v);
if (v==tempV) {
found = 1;
printf("temp v: %lld\n", tempV);
}
i++;
}
if (found==0) {
printf("-1");
}
}