#include <stdio.h>
int func(int n) {
int a = 1;
int b = 2;
int c;
if (n == 1) {
return a;
}
if (n == 2) {
return b;
}
for (int i = 3; i <= n; i++) {
c = 2 * a - 2 * b;
a = b;
b = c;
}
return b;
}
int main(void) {
int n = 5;
printf("a%d = %d\n", n
, func
(n
)); return 0;
}
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