diff --git a/number/exgcd.cc b/number/exgcd.cc
index fdda090..4ca819e 100644
--- a/number/exgcd.cc
+++ b/number/exgcd.cc
@@ -1,3 +1,4 @@
+
 namespace Exgcd {
     struct exgcd_solution_t {
         ll x, y, gcd;
@@ -34,6 +35,22 @@ namespace Exgcd {
         }
     }
 
+    // solve { x = a_i (mod n_i) } if n_i's are coprime
+    optional<ll> crt(const vector<pll>& equations) {
+        ll prod = 1;
+        for (auto&& [a, n] : equations) {
+            prod *= n;
+        }
+        ll res = 0;
+        for (auto&& [a, n] : equations) {
+            ll m = prod / n;
+            auto m_rev = inverse(m, n);
+            if (m_rev == nullopt) return nullopt;
+            res = mod(res + a * mod(m * m_rev.value(), prod), prod);
+        }
+        return res;
+    }
+
     // find minimal non-negative integral solutions of `ax + by = c`
     optional<diophantine_solution_t> diophantine(ll a, ll b, ll c, bool force_positive = false) {
         if (a < 0 || b < 0 || a == 0 && b == 0) return nullopt;