Added brute solution

Unfortuantlly it's bit too slow

Project-Euler/001/bruteforce.c

@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <stdlib.h>
+
+// Use:
+// bruteforce
+// n numbers to calculate (PE 1)
+// number #1 to calculate (PE 1000)
+// number #2 to calculate
+// ...
+// number n to calculate
+
+int main() {
+    int n; 
+    scanf("%d",&n);
+    long arr[n];
+    for(int i = 0; i < n; i++){
+       scanf("%li",&arr[i]);
+    }
+    
+    for (int i = 0; i < n; i++)
+    {
+        long sum = 0;
+        for (long j = 1; j < arr[i]; j++)
+        {
+            if (j % 3 == 0 || j % 5 == 0)
+                sum += j;
+        }
+        printf("%li\n", sum);
+    }
+}