Index: aoc2025.c
==================================================================
--- aoc2025.c
+++ aoc2025.c
@@ -13,18 +13,73 @@
 void aocYYYYDD(char *data, size_t len) {
     (void)len; // unused argument
 }
 
 #endif
+
+/* === aoc202506 =======================================================
+===================================================================== */
+static long long unsigned add2506(long long unsigned v[4][1024], int lin, int col) {
+    long long unsigned sum = 0;
+    for (int k = 0; k < lin; k++) sum += v[k][col];
+    return sum;
+}
+static long long unsigned mul2506(long long unsigned v[4][1024], int lin, int col) {
+    long long unsigned sum = 1;
+    for (int k = 0; k < lin; k++) sum *= v[k][col];
+    return sum;
+}
+
+static long long unsigned input_202506[4][1024];
+void aoc202506(char *data, size_t len) {
+    (void)len; // unused argument
+    char *X;
+    for (;;) {
+        X = strchr(data, '\n');
+        if (!X) break;
+        *X = 'X';
+    }
+    int lin = 0, col;
+    char *err = data;
+    for (;;) { // for each line
+        col = 0;
+        for (;;) { // for each number
+            while (isspace(*err)) err++;
+            long long unsigned tmp = strtoull(err, &err, 10);
+            if ((*err == 'X') && (tmp == 0)) { err++; break; }
+            input_202506[lin][col++] = tmp;
+        }
+        lin++;
+        printf("got line %d with %d columns\n", lin, col);
+        if ((*err == '+') || (*err == '*')) break;
+    }
+    printf("from %llu to %llu\n", input_202506[0][0], input_202506[lin-1][col-1]);
+    col = 0;
+    while (isspace(*err)) err++;
+    long long unsigned sum = 0;
+    for (;;) {
+        switch (*err) {
+            default: /* does not happen! */ break;
+            case 'X': break;
+            case '+': sum += add2506(input_202506, lin, col); break;
+            case '*': sum += mul2506(input_202506, lin, col); break;
+        }
+        if (*err == 'X') break;
+        col++;
+        err++;
+        while (isspace(*err)) err++;
+    }
+    printf("part 1: %llu\n", sum);
+}
 
 /* === aoc202505 =======================================================
 ===================================================================== */
 struct Range {
     long long unsigned lo, hi;
 };
 
-int ascending(const void *a, const void *b) {
+static int ascending(const void *a, const void *b) {
     const struct Range *aa = a, *bb = b;
     if (aa->lo < bb->lo) return -1;
     if (aa->lo > bb->lo) return 1;
     return 0;
 }

Index: aocdailies.c
==================================================================
--- aocdailies.c
+++ aocdailies.c
@@ -4,10 +4,11 @@
 aocfunc *aocselect(unsigned y, unsigned d) {
     aocfunc *p;
     switch (y * 100 + d) {
         default: p = NULL; break;
 
+        case 202506: p = aoc202506; break;
         case 202505: p = aoc202505; break;
         case 202504: p = aoc202504; break;
         case 202503: p = aoc202503; break;
         case 202502: p = aoc202502; break;
         case 202501: p = aoc202501; break;

Index: aocdailies.h
==================================================================
--- aocdailies.h
+++ aocdailies.h
@@ -4,10 +4,11 @@
 #include <stddef.h>
 
 typedef void aocfunc(char *, size_t);
 aocfunc *aocselect(unsigned, unsigned);
 
+aocfunc aoc202506;
 aocfunc aoc202505;
 aocfunc aoc202504;
 aocfunc aoc202503;
 aocfunc aoc202502;
 aocfunc aoc202501;