added euler totient function

Math/eulerTotient.cpp

@@ -0,0 +1,37 @@
+#include<iostream>
+#include<cmath>
+using namespace std;
+
+/*
+this function calculate euler totien function
+*/
+
+long long eulerTotient(long long n){
+    
+    if(n == 1) return 1;
+    long long result = 1LL;
+    long long temp = n;
+    for(int i = 2; i <= floor(sqrt(n)) + 10; i++) {
+        if( temp % i == 0) {
+            int j = 0;
+            while(temp % i == 0){
+                j ++;
+                temp /= i;
+            }
+            result = result * pow(i,j-1) * (i-1);
+        }
+    }
+
+    if(temp == n){
+        return n-1;
+    }
+
+    return result;
+}
+
+int main(){
+    long long n;
+    cin >> n;
+    cout << eulerTotient(n);
+
+}