diff --git a/polynomial.js b/polynomial.js
index 9ae1461..0410cd9 100644
--- a/polynomial.js
+++ b/polynomial.js
@@ -1,14 +1,42 @@
 class Polynomial {
-    constructor(coefArray) {
-        this.degree = coefArray.length - 1;
+    constructor(mod, coefArray) {
+        this.mod = mod;
+        this.degree = (coefArray.length - 1);
         this.coefficients = coefArray;
     }
 }
 
 exports.Class = Polynomial;
 
-function multiply(p1, p2, n) {
+function add(p1, p2) {
+    let n;
+    if (p1.mod !== p2.mod) {
+        throw "different modulo"
+    } else {
+        n = p1.mod;
+    }
+    let len_p1 = p1.coefficients.length;
+    let len_p2 = p2.coefficients.length;
+    result = new Array(Math.max(len_p1, len_p2)).fill(0);
+    if (len_p1 > len_p2) {
+        for (let x = 0; x < len_p1 - len_p2; x++) p2.coefficients.push(0);
+    } else {
+        for (let x = 0; x < len_p2 - len_p1; x++) p1.coefficients.push(0);
+    }
+    for (let i = 0; i < result.length; i++) {
+        result[i] = (p1.coefficients[i] + p2.coefficients[i]) % n;
+    }
+    return new Polynomial(n, result);
+}
+exports.add = add;
 
+function multiply(p1, p2) {
+    let n;
+    if (p1.mod !== p2.mod) {
+        throw "different modulo"
+    } else {
+        n = p1.mod;
+    }
     let f = p1.coefficients;
     let g = p2.coefficients;
     result = new Array(f.length + g.length - 1).fill(0);
@@ -19,11 +47,17 @@ function multiply(p1, p2, n) {
             result[i + j] += f[i] * g[j];
         }
     }
-    return new Polynomial(result.map(x => (x % n) + (x < 0 ? n : 0)));
+    return new Polynomial(n, result.map(x => (x % n) + (x < 0 ? n : 0)));
 }
+exports.multiply = multiply;
 
-function divide(p1, p2, n) {
-
+function divide(p1, p2) {
+    let n;
+    if (p1.mod !== p2.mod) {
+        throw "different modulo"
+    } else {
+        n = p1.mod;
+    }
     let inverse = (x) => {
         for (let i = 1; i < 2; i++) {
             let r = (i * x) % 2;
@@ -51,7 +85,7 @@ function divide(p1, p2, n) {
             tmp.push(0);
         }
         tmp.push(tmp_coef);
-        tmp_poly = new Polynomial(tmp);
+        tmp_poly = new Polynomial(n, tmp);
         let sub = multiply(p2, tmp_poly, n);
         let tmp_f = [];
         for (let i = 0; i < f.length; i++) {
@@ -66,16 +100,17 @@ function divide(p1, p2, n) {
             f.pop();
 
     }
-    return new Polynomial(f);
+    return new Polynomial(n, f);
 }
 
-function gcd(p1, p2, n) {
+exports.divide = divide;
+
+function gcd(p1, p2) {
     if (p2.coefficients.length === 0) {
         return p1;
     }
-    return gcd(p2, divide(p1, p2, n), n);
+    return gcd(p2, divide(p1, p2));
 }
 
-exports.multiply = multiply;
-exports.divide = divide;
+
 exports.gcd = gcd;
\ No newline at end of file