SimpleLoop

int adpos = 2;
int step = 0

for(int i = 0; i < array.count; i++) {
    id object = array[i];
    if ([object isKindOfClass:[RelatedNewsListModel class]]) {
        if (step == adpos) {
            [array insertObject:[DFPNativeModel new] atIndex:i];
            step = -1;
        }
        step++;
    }
}