diff --git a/template.cc b/template.cc
index 92b5fcd..e0ac325 100644
--- a/template.cc
+++ b/template.cc
@@ -279,6 +279,16 @@ return_t qpow(ll b, ll p) {
     else return half * half;
 }
 
+// dynamic modulus
+ll qpow(ll b, ll p, ll mod) {
+    if (b == 0 and p != 0) return 0;
+    if (p == 0) return 1;
+    ll half = qpow(b, p / 2, mod);
+    if (p % 2 == 1) return (int128(half) * half % mod) * b % mod;
+    else return half * half % mod;
+}
+
+
 // Accurately find `i` 'th root of `n` (taking the floor)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wparentheses"