diff --git a/du3/program b/du3/program
index ed77f5f..e021d85 100755
Binary files a/du3/program and b/du3/program differ
diff --git a/du3/program.c b/du3/program.c
index a3e22ef..c6ffa0c 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -5,32 +5,84 @@
 #include<time.h>
 #include<stdlib.h>
 
+#define max_yr 9999
+#define min_yr 1900
+
+int isleap(int y) {
+   if (y % 4 != 0) {
+      return 0;
+   } else if (y % 100 != 0) {
+      return 1;
+   } else if (y % 400 != 0) {
+      return 0;
+   }
+
+   return 1;
+}
+
+int datevalid(int d, int m, int y) {
+   if(y < min_yr || y > max_yr) {
+      return 0;
+   }
+   
+   if(m < 1 || m > 12) {
+      return 0;
+   }
+   
+   if(d < 1 || d > 31) {
+      return 0;
+   }
+
+   if(m == 2) {
+      if(isleap(y)) {
+         if(d <= 29) {
+            return 1;
+         }
+      } else {
+         return 0;
+      }
+   }
+
+   if ( m == 4 || m == 6 || m == 9 || m == 11 ) {
+      if(d <= 30) {
+         return 1;
+      } else {
+         return 0;
+      }
+   }
+
+   return 1;
+}
+
 int main() {
-    char buffer[20];
-    struct tm tm = {0};
+   char buffer[20];
+   struct tm tm = {0};
 
-    char *retval = fgets(buffer, sizeof(buffer), stdin);
+   char *retval = fgets(buffer, sizeof(buffer), stdin);
 
-    if (retval == 0) {
-        puts("Neplatny datum");
-        return 0;
-    }
+   if (retval == 0) {
+      puts("Neplatny datum");
+      return 0;
+   }
 
-    retval = strptime(buffer, "%e.%m.%-Y", &tm);
+   retval = strptime(buffer, "%e.%m.%-Y", &tm);
 
-    if (retval == 0) {
-        puts("Neplatny datum");
-        return 0;
-    }
+   if (retval == 0 || datevalid(tm.tm_mday, tm.tm_mon + 1, tm.tm_year + 1900) == 0) {
+      puts("Neplatny datum");
+      return 0;
+   }
 
-    tm.tm_isdst = -1;
-    tm.tm_mday += 7;
+   tm.tm_isdst = -1;
+   tm.tm_mday += 7;
 
-    mktime(&tm);
-    
-    strftime(buffer, sizeof(buffer), "%e.%m.%-Y", &tm);
-    puts(buffer);
-    putc('\n', stdout);
-    
-    return 0;
-}
\ No newline at end of file
+   if (mktime(&tm) == -1) {
+      puts("Neplatny datum");
+      return 0;
+   }
+   
+   strftime(buffer, sizeof(buffer), "%e.%m.%-Y", &tm);
+   puts(buffer);
+   putc('\n', stdout);
+   
+   return 0;
+}