int modPow(int base, int exp, int n) {

base = base%n;

if (exp == 0)
    return 1;

else if (exp == 1)
    return base;

else if (exp%2 == 0)
    return modPow(base*base%n, exp/2, n);

else
    return base*modPow(base, exp-1, n)%n;