if$($n$<0)$

return $-1$;

$//$declare int variable term$1,$term$2$ and nextTerm

$//$initialize term$1,$term$2$ with $0$ and $1$

int term$1=0,$term$2=1,$nextTerm;

$//$for loop iterate n times

for$($int i$=1$;i$<=$n;i$++)$

$\{$

$//$nextTerm is calculated by adding term$1$ and term$2$

nextTerm$=$term$1+$term$2$;

$//$set term$2$ value as new term$1$

term$1=$term$2$;

$//$set nextTerm value as new term$2$

term$2=$nextTerm;

$\}$

return term$1$;

$\}$