Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -8,26 +8,48 @@
 #include "aocutils.h"
 
 /* === aoc202407 =======================================================
    Part one looks easy
 ===================================================================== */
+
+static unsigned long long concat(unsigned long long a, unsigned long long b) {
+    unsigned long long r = a, t = b;
+    while (b) {
+        r *= 10;
+        b /= 10;
+    }
+    return r + t;
+}
 
 static bool canbetrue(unsigned long long v, unsigned long long *a, size_t n) {
-    // for startes let's assume no overflowing
+    if (n == 1) return (v == *a);
+    unsigned long long tmp = a[1];
+    a[1] = a[0] + tmp;
+    if (canbetrue(v, a+1, n-1)) { a[1] = tmp; return true; }
+    a[1] = a[0] * tmp;
+    if (canbetrue(v, a+1, n-1)) { a[1] = tmp; return true; }
+    a[1] = tmp;
+    return false;
+}
+
+static bool canbetrue3(unsigned long long v, unsigned long long *a, size_t n) {
+    // still, let's assume no unsigned long long overflowing
     if (n == 1) return (v == *a);
-    unsigned tmp = a[1];
+    unsigned long long tmp = a[1];
     a[1] = a[0] + tmp;
-    if (canbetrue(v, a+1, n-1)) return true;
+    if (canbetrue3(v, a+1, n-1)) { a[1] = tmp; return true; }
     a[1] = a[0] * tmp;
-    if (canbetrue(v, a+1, n-1)) return true;
+    if (canbetrue3(v, a+1, n-1)) { a[1] = tmp; return true; }
+    a[1] = concat(a[0], tmp);
+    if (canbetrue3(v, a+1, n-1)) { a[1] = tmp; return true; }
     a[1] = tmp;
     return false;
 }
 
 void aoc202407(char *data, size_t len) {
     (void)len; // unused argument
-    unsigned long long calibrationtotal = 0;
+    unsigned long long calibrationtotal = 0, calibration3total = 0;
     char *line = strtok(data, "\n");
     unsigned long long number[50], nnumber;
     while (line) {
         char *err;
         unsigned long long testvalue = strtoull(line, &err, 10);
@@ -34,14 +56,20 @@
         err += 1; // skip ':'
         nnumber = 0;
         while (*err == ' ') {
             number[nnumber++] = strtoul(err, &err, 10);
         }
-        if (canbetrue(testvalue, number, nnumber)) calibrationtotal += testvalue;
+        if (canbetrue(testvalue, number, nnumber)) {
+            calibrationtotal += testvalue;
+        }
+        if (canbetrue3(testvalue, number, nnumber)) {
+            calibration3total += testvalue;
+        }
         line = strtok(NULL, "\n");
     }
     printf("The calibration total is {%llu}.\n", calibrationtotal);
+    printf("The calibration total with three operators is {%llu}.\n", calibration3total);
 }
 
 /* === aoc202406 =======================================================
    Hmmm, I've done something like this already this year... on day 4
    I need rcmap() moved to aocutils ... done; now it's called `linearize2d`